I was generating a skill (design guide), and was updating an artifact as living proof. I kept running into the same issue, thinking the skill was just not able to be generated properly.

However, the AI gave this feedback at some point:

The problem before was that artifact builds snapshot the skill at clone time, so even though I kept updating the skill, the artifact kept using the old cached version. I had to delete the snapshot and force a fresh build. Should be sticking now.

This actually didn't work. So I created a new artifact, which was good. So skill was awesome! However cache got in the way and that is not convenient while adjusting a skill and trying to see the proof in an artifact.