I've no personal empiric evidence that level busts are fatigue related but it would seem reasonable to look into fatigue as a contributary factor.
I've said it before and will say again:
1. 320 and 330 can sound very similar on RT.
2. If ANY crewmember expresses doubt about the cleared level ask again and keep asking until there is no doubt. If, as an FO, you are flying with 'one of those captains' don't ask him if you should reconfirm with ATC - just do it (he can't then tell you not to). Embarrassment is transient - death is permanent.