Remote access doesn't work, local access does

[RemoteUser1138istheGOAT]

After yet more troubleshooting, I think I figured it out.  Maybe.  Still needs testing.

The problem all along seems to have been with a commercial VPN application I was running on the host machine. 

To be clear, this is used to access a commercial VPN service, this is not the same as the VPN server running on my router (which is used to allow remote clients secure "phone home" ability).  I did not think to mention it before, because it did not occur to me (or anyone else, apparently) as relevant.

That commercial VPN application has a feature to allow access to local subnets (outside the VPN pipe, if you will) while connected to the VPN, but it's buggy.

Once I disconnected from the commercial VPN service, remote clients (using the Ubiquiti VPN server) were able to access Jellyfin again.

I don't always have the Jellyfin host machine connected to the commercial VPN.  I believe that the seemingly-random periods of Jellyfin access working or not, mentioned above, were exactly those periods.

I'll do more testing and post a follow-up in a week or two.

I made this account solely to thank you friend. After many turns and Google gemini queries and going in circles you saved me from spending time and remaking my jellyfin server because honestly it would've led to that, as I completely forgot I too had a VPN running on the server itself, so basically I was having two VPNs battling it out like two raccoons on Thanksgiving night for the last piece of wishbone. I was using it to transfer files from my jellyfin to a cousin's jellyfin server and completely forgot about it. sorry it took you having to ultimately break your head over it like I nearly did but you are a hero and im sure this post will help the odd fellow here and there who have this exact thing happened to them lol  have a blessed day/night.