The World of Avlis

Yep... What the bug seems to be is that an enemy gets shuffled out of your attack range some how, and instead of it resolving by canceling that stage of attack, your character goes "!!! NOT THERE ANYMORE!" and freezes because it's unable to continue the process... Apparently canceling the action in ...

Yeah what it is a game mechanic, involving one of the uses of the Listen. Your game is telling you 'hey you heard an invisible creature here, and this is what it looks like'. I, too, am exceptionally aggravated by it. You'll need something that lets you See Invisibility to get around it.