So I switch service provider rebuilt my supernode. After it finishes I tried to start delegate harvesting for account NAFDZB-OFPCDY-WRSJLR-MPUYXU-U4CIQ4-IPLJBB-RN4K “Error 306 NIS: Unexpected Error”. I have another account and I can start without problem on the same node. I tried to switch to another node but same problem.
Edit: The delegate keys had changed for some reason. Problem solved after correcting the keys in config files