I'm not even sure if the players are supposed to get max chemistry when fully upgraded. Whenever I close my game, my Huijsen (and even my toty donnarumma for some reason) lose their chemistry points. Huijsen goes from 3 to 0, Donna goes from 3 to 2. When I wait couple minutes before going to a match, I get a message that says "there is a problem with chemistry. Press ok to fix it" and it gives them the chemistry back. Also whenever you skip the starting cutscene when going to a match, the game throws you out of the match.