I was working on a Windows 10 PC connected to a domain. This PC could be pinged by DNS name and IP address. RDP was also working. There were no other issues on network. No domain policies were in place that should have been keeping PC admin shares from working. But it was still failing after registry settings changes, removing and re-adding to domain, etc.
I found an article about shares not working if there is a misconfigured DNS entry somewhere. I looked on the secondary DNS server and there was an old, incorrect entry for that PC. Removed the DNS entry and shares began to work.