On the right side of the training filed, you can't see all the players (if you have more than 76 (19 lines * 4 slots per line) coaches & senior players) .
I have a lots of coaches & senior players (more exactly 77). I removed the player with highest number(99) from the filed and put in on the right. He was gone from the page and i couldn't put it back on the field. I had to find a trick to put it back on training (change it's squad number to a lower value, and he appeared).
If an xA is reading this, please put this bug on the admin forum so that the crew can fix it; probably there is a limit to maximum 19 lines and it should be increased.