On my R7 & R8 the smaller square in the middle indicates your autofocus mode and that'll get bigger, small, rectangular, box with boxes around it etc depending on what you choose. That large white frame of four corners is what the AF is currently tracking, it should move around if you move the camera or if something else gets its attention (like Waddizzle mentioned). If you immediately pressed the shutter that would be your focus point. It's actually a nice feature where if its already sitting on a particular face, bird or airplane I want to snap then you don't have to go half shutter to lock it, you can be confident it is and will be focused on whatever the four corners surround. It follows kids around really well if you're waiting for that great shot and don't want to hold half shutter for three minutes.
The green rectangle in the next pic means you went half shutter and locked it. The green means single shot and if you select AI Servo (which I love on these mirrorless R-series cameras) that box will be blue and will continue to move with the subject (completely awesome and appreciated) while the green will stick with that focal point (not as awesome unless you're shooting stationary objects... but even then I'm lazy and use AI Servo).
The ONLY time I'm not in AI Servo (blue boxes) is if there are too many faces or something it is biting off on when I'm trying to just get an object in the middle of people or closer objects. If you can reprogram the R50 I actually customized a seldom used button on the R7 & 8 to switch between AI Servo and single shot to make the transition quick and easy. Honestly AI Servo gets exactly what I want 98.6% of the time but that 1.4% of the time can be frustrating if you're not quick and comfortable switching modes (I finally programmed the button because I missed a handful of great shots, but I know I'd have missed 98+% more great shots if I hadn't been in AI Servo, it's amazing).
Play with it a bit and see if it behaves like I'm explaining. I don't have an R50 but I can't imagine they're doing it different.
* I just edited this because as I was typing and telling you to sort your AI Servo mode solidly I also realized that if you learned to watch and trust the white four cornered rectangle you're seeing what the AI Servo would be doing with a half shutter that generates the blue boxes... keep playing with it and you'll eventually love and trust it. If you do find that it keeps locking things you don't want just shrink the AF area until it doesn't inspect so much of the frame. I program my lens control rings to switch AF modes so I can quickly dial down to a tiny square if it isn't behaving or spin over quickly to horizontal pan if a jet is whizzing by then back to a medium AF square for default walk around mode. As you learn the camera and sort what frustrates you (like rapidly changing autofocus modes) you can use that clever lens control wheel to make it easy.
A friend of mine uses the lens wheel for aperture and that may even be default but I'm so used to switching aperture with a finger wheel and I realized autofocus mode was the one thing slowing me down between shooting people, planes, puppies etc so I used the wheel for that. Autofocus mode is exceptionally important to master now that the camera is doing so much of the choosing. You'll love it, but you have to understand and master it or it'll frustrate you randomly.
** Editing again cause I hadn't seen that you have an R6 as well. All of the above still pertains but if you're not seeing it on the R6 then it may be one of the newer firmware features or a deeply hidden menu item that is on by default in the R50 and not the R6. I fired up my R8 and it does white four corner tracking before half shutter but the R7 didn't (thought it did, but since I'm always chasing the AI Servo blue boxes I don't give it a chance to do the white corners often enough). Firmware, menus, who ever knows...
Happy Autofocus Shooting!!
Chris
