So yeah, ok, he have a 355% in a skill, but this isn't the cause of the general ratings drop. The cause is the previous training you did that wasn't counted and it caused some kind of issue in the upcoming match simulation.
I had a situation like this too, after abig invertment all the team changed it's behavior. The player I had that scored 5/5 FKs stopped scoring, the one that assisted in corners, stopped assisting, the key players changed radically yhe behavior after a big investment...
That's why sometimes isn't as easy as it seems to select a player where to invest the resources...
As said please, contact the support and ask them fopr a check out.
Cheers,
Khris