Usually happens when completing a raid and getting the hero of the village effect. Usually happens in this order:

I trade with Villager (there's 1 in my base) without raid happening yet and without bad omen

Finds pillagers and gets bad omen effect

Returns home only to start a raid

Dies at least once

Completes raid and receives Hero of the Village

Goes to trade with Villager but trading inventory opens for a split second then closes