Sorry, looked at my AST again and I think it was actually Dusk Vigil that gave me issues. I'd have to replay it again (I've been busy and haven't touched it in a while), but one of the bosses was giving me trouble, so I left Nocturnal and went back to Diurnal. For some reason I was thinking I hadn't hit 50 with AST yet.
Although I did have some gear issues in Aurum Vale previously.