This is when one player has a turn with Angels, and the other player has a turn with Gnolls in a battle against each other.
Ah, now everything is perfectly clear!
What is the reason for this phenomenon? According to the rules, you should contact the organizers and, possibly, replay the battle. But how do you remember/prove the sequence of turns in a battle before the desynchronization? I didn't find anything specific in the rules, and I haven't encountered this phenomenon myself.