This happens when the client can’t find their contact list. It’s dangerous to create a new one because this could wipe out their contact list from somewhere that may be temporarily down.
Damus has a First Aid feature in settings to recover from this.
No, but there was/is overlap. I’d only expect using different relays in the two apps to mean there is some (hopefully temporary) inconsistency between the follow lists in the two apps. But like @Crizzo said, new accounts should work out of the box. 😊