Please describe in as much detail as possible how to reproduce the bug or crash.
When enemy creature has some immunities on artifact, the immunities stay with creature even after artifact is destroyed by Decay spell.
It will no longer show “Immune (Artifact)” text but the debuffs will not be applied to the creature.
Not sure this applies to all types of immunity or not.
Not sure this is the case for traits that grant immunity too or not.
What game version are you playing? You can find the version number on the title screen in the lower left corner.