... could be caused by cheating

[lch]

Misinformation... The client can't usually play a turn with a lower version number than the turn file that he got from the server. What kind of mods are loaded depends solely on the game being played. Outdated mod files with the same name as the newer ones can be a problem, though, yes. Most usually this is an unexpected thing like removing units from building queues of forts that have been taken over or stuff like that, at least that was often the case in earlier games. It might be something similar to that now.