Once the prevent damage is removed the creature still receives no damage when attacked. Damage spells still work on it without issue.
Based on your title Razia had first strike in this example, correct?
Is it possible that she was killing attacking creatures with first strike damage, and thus not taking regular attacking damage? If so that is not a bug, that is working properly
She didn’t have first strike. There was no evergreen or buff present. No Adjacent monster ability or support to give her first strike.
Oh. Then where was the first strike? On your opponent’s creature?
Huh. That does sound like a bug then. Sorry.