Okay, so you're relatively new using the 7DII and much of your previous experience has been with T3i, T5i and 60D. All three of those cameras use a considerably simpler 9-point AF system than the 7DII.
You also mention using 5DIII and 5DIV, which have AF systems more similar to 7DII. (But it sounds as if the 5DIII/IV are being used in a limited way, for specific types of subjects... see below).
Two things I noticed is that you have the 7DII set to One Shot and have Intelligent Tracking enabled.
I'm not entirely certain which focus pattern you are using... You mention All Points (65)? 4-Point Expansion? Single Point? Or maybe you're switching between those? Regardless, I'll get into these in more detail below.
INTELLIGENT TRACKING:
The primary purpose of Intelligent Tracking (iTR) is to recognize the face of a person and track it's movement. Is that how you are using it? If so, you need to have the camera set to AI Servo and either use All Points or Large Zone focus pattern. If not using iTR for shots of people who are moving (or if you and your camera are moving), I'd recommend turning it off. Personally, shooting with two 7DII for about a year, I haven't used it at all. I'm not ruling out using it, but generally prefer to control where the camera focuses myself and not rely too much on the automation.
ONE SHOT AF versus AI SERVO AF MODE:
Are your problem shots primarily with moving subjects? I wouldn't be surprised, if you're using One Shot mode all the time. One Shot is for stationary subjects. It acquires focus, then stops, locks and gives you "Focus Confirmation". That's great when the subject isn't moving... But if the distance between you and the subject changes because either you or the subject or both are moving, the focus will be off. To re-focus you have to lift pressure off the button and re-apply it.
AI Servo is for moving subjects. Set to this mode, the camera and lens acquire focus, then continues to run continuously as long as you maintain pressure on the button, updating focus constantly. It never stops and locks... and it can't give Focus Confirmation.
It may be different types of subjects and these focus modes where you are having success or problems. For example, shooting weddings with a 5DIII or IV might often be best done with One Shot... While shooting sports or any other type of action with a 7DII requires AI Servo.
I think all Canon cameras have a Focus Confirmation "beep" that the user can turn on or off. I leave this enabled because it immediately alerts me if I've left my camera set to One Shot, and warns me to change it if I'm now photographing a moving subject. I often hear other peoples' cameras "beeping" when I'm shooting sporting events with moving subjects.... and can pretty much guarantee that they'll have a high percentage of missed-focus images.
Many Canon have a third focus mode: AI Focus. Personally I never use it. This mode leaves it up to the camera to decide whether or not the subject is moving, then it's supposed to switch to use One Shot or AI Servo, whichever the camera "thinks" is appropriate. Maybe it's better now, but in the past when I experimented with this on earlier camera models I felt it added a slight delay and sometimes chose incorrectly or failed to switch if a subject started or stopped moving. I prefer to set the focus mode myself. I get a higher percentage of in-focus shots that way. (Note: it might be a hint that the most advanced, pro-oriented 1D-sereis models don't even offer AI Focus mode... they only have AI Servo and One Shot.)
FOCUS PATTERNS:
Your T3i, T5i and 60D all only had two patterns to choose between: Single Point/Manual Selection or All Points/Auto Selection. The 7DII has those as well, plus five additional patterns (Large Zone, Zone, 4-point Expansion, 8-point Expansion and Spot/Precision Focus), making your choices a lot more complex.
Personally my rule of thumb is to use as few AF points as possible. I use Single Point much of the time... occasionally switch to Spot/Precision for certain uses or one of the Expansion or smaller Zone pattern in some special circumstances where they are useful. Single Point puts me more fully "in charge" of where the camera focuses... but it also means I have to work harder to keep the AF point right exactly I want camera and lens to focus.
I call Spot/Precision Focus my "Birds in Trees" mode, as that's an example when it can be really useful. This setting is also Single Point, but uses a smaller than usual, more precise AF sensor point. It's handy when trying to photograph through a tangle of branches, where a larger AF point would be distracted by branches between me and the subject, for example. Of course, it's useful for a lot of things. Some folks prefer it for portraiture. I think it's a little slower than standard Single Point, maybe a bit less useful for rapidly moving subjects. But I also know of people using it for butterflies and small birds in flight, so it's no slouch.
I use one or the other of the Expansion Point modes sometimes when shooting erratically moving subjects that may change direction unexpectedly, making them difficult for me to keep a single AF point right on the subject. If it's a subject moving in either horizontal or vertical plane only (example, a running person or animal), I'll use 4-point Expansion which enables the points to the left and right, above and below the primary point. If there's a chance the subject may change direction more freely (such as a bird in flight), I'll use 8-point, which enables those same four plus the four AF points immediately diagonal to the primary point. Both Expansion Point modes always start with a single point which you select, much the way you do with Single Point or Spot Focus. However, Expansion allows those surrounding AF points to "take over" if you can't keep the selected point right on the subject. This works pretty darned well in many situations, but if I can use Single Point instead, that will always give me the highest percentage of acceptably focused shots.
Either Zone focus pattern is sort of like smaller version of All Points/Auto. When set to that, you can choose the general area that will be active, but not a specific AF point. These patterns leave it up to the camera to choose. I mostly use the smaller Zone.. but even that not a lot. It's most ideal for things like "Birds In Flight", when the subject is flying against a plain background such as a cloudless sky. If there's a lot of separation between subject and a busier background, it can work pretty well too. But with this pattern you are leaving it up to the camera to choose and it will usually pick an AF point that's covering the closest object. This can work fine with a bird flying directly toward you, for example, focusing upon it's beak. But with a bird flying at a diagonal or across your field of view, it might focus on the closest wing tip and cause the bird's eye and body to be slightly out of focus.
I use Large Zone far less and almost never use All Points/Auto. For me, these patterns just just leave too much to up to chance where the camera and lens will focus.
OTHER SETTINGS AND STUFF THAT MIGHT HELP:
Back Button Focusing is a popular technique among sports photographers, in particular... though it can be used for almost anything. BBF removes the AF function from the shutter release button, so that AF is only controlled by the "AF ON" button on the rear of the camera, under the photographer's thumb. This puts me more in control of starting and stopping AF.
There are times, such as focus and recompose, when AI Servo can get you in trouble and cause missed focus shots. However, using BBF solves that and allows me to use AI Servo as my default mode, for both moving and stationary subjects. You might want to try it and it's easy to set up. Just go into the menu, to the control customization and assignment page... navigate to the shutter release button (the first item) and change it to the middle "Meter' setting. This disables AF there, but leaves it at the AF ON button, which you'll be able to control with your thumb. (It's also optionally possible to switch the functions of the AF ON and the */AE Lock buttons.)
Lenses and their settings can also make a difference in AF performance. For one, ultrasonic focus drive "USM" lenses (also Tamron USD or Sigma HSM) are the fastest and you can manually override focus at any time with them, with no harm to the lens. Stepper motor or "STM" lenses are pretty good, but not quite as fast focusing, but are typically quieter and smoother running (so are desirable for video, in particular). STM also can be manually overridden safely, but the lens' AF must be "powered up" because it's a "fly-by-wire" system... there's no direct mechanical linkage between the focus ring and the focus drive motor... it's electronic. A half-press fo the shutter release or holding the AF ON button powers up the lens' AF. When it's not powered up, turning the manual focus ring won't do anything. Micro motor lenses are the third type (Canon's are not marked STM or USM...other brands may call them "Piezo" or "PZD"). Those are typically slower and noisier focusing. They also should not be manually overridden without first turning off AF at the switch on the lens. Failing to do that can damage the lens' focus mechanism. Most of your lenses appear to be USM type, which is good!
The lens' maximum aperture can make a difference in AF performance, too. A larger aperture allows in more light for the AF sensors to work with. An f/1.4 lens allows in four times as much light as an f/2.8, for example. However, a larger aperture also makes for shallower depth of field, which can require more precise autofocusing. Setting a smaller aperture for the exposure (lens only stops down at the very instant of exposure) can help with that, can be a little more forgiving of minor focus errors. So unless you're trying make a background blur strongly, try selecting a one or two stop smaller aperture. This can be more critical with longer focal lengths than with wide angle lenses. Telephotos just naturally render shallower depth of field.
Some zoom lenses are varifocal designs, too. This means they don't maintain focus when the focal length is changed. The problem with these can be that you must re-focus after any changes are made with the zoom. If using One Shot, you have to make a point of releasing the button, then reapplying it. But if using AI Servo, the system will automatically correct focus. (Other zooms are "parfocal", meaning they maintain focus when zoomed. But today a lot are varifocal because it's less complex and expensive to make them... and autofocus can quickly correct focus anyway.... assuming it's used correctly.)
Keep practising with the 7DII... The "Active Matrix" focusing screen is different from the fixed screens in your T3i, T5i and 60D... It can take a while to become accustomed to using that and learn to "trust" the camera and yourself, especially when using AI Servo mode (where there's no Focus Confirmation)!
You mention using Live View, too. Be aware that's a completely different auto focus system in your DSLRs. The "normal" viewfinder-based AF uses an array of sensors (those 65 AF points). Live View uses the image sensor itself. The 7DII has a much improved Live View focusing technology... but it's still not as fast as the viewfinder-based system.
There's more, but the above covers most of the "basics". I'd recommend not getting into some of the "fine tuning" until you feel more comfortable with the camera and can experiment with each of them a little at a time.
For example, the 7DII has Micro Focus Adjustment feature, which allows you to fine tune the focus of up to 40 specific lenses to your particular camera. I'd suggest you don't get into this until you know for certain that a lens is off a little and the fine tuning is necessary. See the manual... there's a specific procedure to do these very precise adjustments (or softwares that can help, such as Reiken FoCal).
Hang in there and don't give up! I came from using a pair of the original 7D for about five years, upgraded to a pair of 7DII last year. That was a pretty easy transition, because the original 7D's AF system is pretty similar, although it has far fewer AF points (19 versus 65 in the 7DII).
it was much more of a challenge for me when I first got the original 7D cameras. I was coming from cameras more similar to your T3i, T5i and 60D (in my case it was 10D, 30D, 50D and 5D Mark II, primarily). I really struggled at first, to learn to use the new, much more complex and sophisticated 7D system well. It wasn't made any easier at the time, either, that the system was new to everyone... no one could advice me and there weren't any guide books written about it. I almost gave up and went back to my old cameras! But I persevered and eventually learned to use the new system with very good success. I now expect and regularly get acceptably accurate focus on 95% or better of my shots (and the ones that miss... probably at least half are my fault, not the camera's).
Speaking of which, when I get a new camera I always make a point of getting one of the guide books for it. Reading that and studying the user manual help me get up to speed with the camera as quickly and painlessly as possible. Canon included an abbreviated user manual with my 7DIIs (about 150 pages)... but there's a more detailed PDF version available for download (about 500 pages), as well as a separate downloadable manual just covering the AF system (approx. 50 pages). There are several guide books avalable now, too. Those can help expand upon the user manual and might be helpful. I bought the "Dummies" series and wasn't all that impressed with it. (But it was the only guide available when I got my cameras). Maybe the book by Doug Klostermann or Jeff Revel is better... check reader reviews. I've bought and liked other guide books by David Busch, but his 7DII guide appears to only be available as a Kindle (which I don't have).
Hope this helps!
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2) some other cameras, various lenses & accessories
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