USB Share not accessible when WAN is down

Welp, seems I got the share to work as expected with the WAN cable unplugged. Darned if I can fully explain why, but here's what I did...

I noticed in Windows Networking that my Sony 4k player UBP-X800 was still connecting via wireless from the last time I had it check for firmware updates. It showed as a media player and media source. Looking into the settings on it, apparently by default it had enabled it's media server and also network access control using UPNP. I turned all that off, and disabled the wireless conection on it so it no longer was connecting. I then turned on, then off, UPNP on the router under Advanced settings, which seemed to do a long reset each time. I'm guessing it was resetting some kind of networking cache and in the process flushed out the bad junk from the Sony player. If I had to guess, the Sony player was doing some kind of loop on UPNP bogging down other services....maybe.

I'm glad that my previous suspicion that the router was disabling SMB share functionality when WAN is down was wrong. Thanks to all who put time in to help work through this.