the improper planning of fixtures (matches too close to each other, 2-3 matches a day)
well, that's an issue because in the game there is participation from players all over the world.
A better grouping in servers, among players with similar time zone is a solution but it would be interest to play with a manager from US ,Brazil or Japan too.
As I said, one solution is to "stock" condition over 100% and more details in auto subs - 11 positions.