There seems to be progressive fatigue in the game. In the 4th quarter most players are yellow for me. Though the color is misleading...yellow still seems to be in the 90s or so.
And that is the reason players disappear. This year pre patch it seemed to happen far less frequently than years past, but post patch it seems to be far less. But if you set sub in/out at 98/95 like many did in years past...the rb would never recover higher than 98 at some point so wouldn't come back. It wasnt a matter of auto subs not working. It just seemed fatigue wasnt consistent. This year seems to be better (hence a lot of people saying auto subs are "fixed")