When stacking 8 switches, all of them *unconfigure switch all* and out of the box... So they have never had ANY CONFIG. Some switches show this when you run show licence
You see Feature Packs: DirectAttach
This causes members of the stack to fail to join with a licence error. Not sure what DirectAttach is or why its installed. But I had to do a clear licence on all switches before the stack would be stable at all.