EF 100-400mm f/4.5-5.6L IS II USM Autofocus suddenly not working

[canonbirds]

Had this lens since Sep 2019 and worked beautifully for about 6-7 months and I've started noticing issues with it's AF for a couple months. 

I mainly shoot birds, f/5.6 to f/8. IS mode set to 2 on the lens for movement. AI Servo on the camera body. Av mode on the camera body so it chooses the shutter speed, I only change the f-stop sometimes and possibly the ISO but not much (maybe 2-400). Like I said, it worked great for months and months had no issues.

Now with everything being exactly the same and still using multiple point AF it will not consistently focus on the bird I'm aiming directly at and clearly have in my sights. Press the shutter halfway down, you can hear the motors in the lens trying to work and it just doesn't focus on the subject anymore. Every now and then I might get lucky based on proximity.

I called Canon today and was on the phone 20 minutes explaining the issue. He said I would receive Emails with directions on mailing the lens to them. He repeated my Email address back to me perfectly and I have not received any notifications.

Should I clean the lens without the caps off in any way? Should I do anything before sending it or taking it to repair? Any help anyone can provide is much appreciated. I've taken great care of it and I kind of expect a $2k piece of equipment to work properly. 

[canonbirds]

I'll have to make some notes on what my settings are currently before I jump straight into a factory reset. Then I'll do it and go snap some shots

Thanks for everyone's replies

[ebiggs1]

"I may try that at some point with the custom settings."

Yes stop!  You need to get back to square one first.  Do the reset and the daylight outdoor test.

"I still feel like it may be a camera setting I changed..."

You are right and you are going to chase your tail unless you start over.

[ebiggs1]

"I'll have to make some notes on what my settings are currently ..."

There is little reason to do that.  They are wrong.  Most of the time the camera knows what to do.  People get into trouble when they tell it to do differently.  Don't try to over think a simple task.  Please do the reset and test.  If nothing else it will assure you that the camera/lens is working as it should.

[canonbirds]

I appreciate you responding and trying to help, truly I do. The custom settings is not something I'm going to do now, I'm well aware that was advice he was giving me to try out in the future. I guess I have come across as slow or ignorant so I apologize for not communicating clearly but your last messages are somewhat patronizing. 

It's not an exercise in futility to jot down current camera settings if I'm going to reset the camera; there are settings that have nothing to do with the lens autofocus that I may forget if I don't write them down. I just did it, it took about 15 minutes, and it gave me needed perspective. I can still reset the camera settings, what harm did that do? 

[ebiggs1]

"...what harm did that do?"

Nothing, it's your camera. The advice is just a suggestion of what I have seen work over decades of photography experience.

"Autofocus suddenly not working"

This was the question, the reset confirms only that the camera/lens is working properly and the problem exists elsewhere.

Ultimately you have to do what you deem is right.