I didn't respond because I don't really actually know what to say to you!
I thought others would maybe give their thoughts but it seems not.
I really never tried putting my players to rest in the season so I can speak about that. In the 9 years I've been playing EHM I always put my players with a practice schedule. It probably helps them but also, the team chemistry is important. Sometimes a group of player will play average together and others will put up amazing performances together. Even just switching one player to another line can make the difference. So maybe you simply have the right combo in your hands.
I know I didn't really answered your question but IMO it's not a bug judging by how the game works sometimes.