I have noticed this very recently after the last patch, so I'd assume a bug.
I have multiple manager careers, post-patch loading one after a week not playing. I simuluate a few games, when I suddenly notice FOUR of my players losing one point OVR rating, although they are NOT too old.. all players in the career came from own youth academy and the oldest is 25 ! They are NOT supposed to lose points this early age, don't they?
I have started to observe it, and see it in other careers as well... I know 100% that a player had a specific rating, when suddenly he has 1 point less...
Secondly, another career, again with 100% youth players... mulitple players in the academy reach a new OVR rating, but when checked in team statistics, they still have the old rating. I have players trains THREE times to the same rating and they keep droping back.. wtf?