I’m not sure which bug you’re referring to, but I can describe two that happen quite frequently.
The first is the “Opponent doesn’t attack” bug, where the enemy is either faster than you or has a turn 1 priority move (like Eremotherium’s Camoflage), but the enemy just doesn’t attack. This has been around for quite a while and a couple bug reports have been made about it.
The second is exactly what @Snake_Dude described, the “No delay” bug, where a creature uses a move on turn 1 that’s supposed to be delayed by a turn. This one popped up more recently and is quite a pain to deal with.