Just found out that if you use a youth player for senior games, once they'll return to the youth team they will be marked as 'unavailable' for the youth team games.
so I used 4 of my best youth team players for a cup games in September, and now it's January and I found out they haven't played since, for no reason other than being marked as unavailable
so frustrated, thinking about abandoning the save (I'm doing great) and start over. it's just doesn't seem fair for those players to not participate and improve.