In Career Mode, using a preset playing style and hiring the corresponding coaches will gain your players a rating boost of for example +3 or +4.
However, when I start a match, my active tactics and player boosts seem to disappear. When I go to the "Team Management" tab in the menu, all rating boost are gone. If I then go the "Tactics" tab, my active tactic is grey, like it's not active at all. I then choose to activate it and the player boost appears again in the "Team Management" tab. Unfortunately, if I then return to the match and immediately (or after a while) go back to the "Team Management" tab, everything is reset again.
I noticed on Reddit a topic with 20 upvotes that covers the issue, so I'm not the only one. Hopefully this can be resolved in the next update!
Link to Reddit topic: https://www.reddit.com/r/FifaCareers/comments/1houao6/whats_wrong_with_my_players/
