Having the same issue with Remote Access, everything seems correct and settings for remote access says “Fully accessible outside your network”. Its not! wiped and reloaded server, installed most current version of Plex and rebuilt router port forwarding table. Going to try going back to and older version of Plex.
I’ve had a different issue over the last three versions where my Windows server wouldn’t tune or pull a stream from my tuner. My 2nd Qnap server works just fine over the last three versions.
The Windows server only works properly on the 1.18.1.2019 release. I wonder if this is somehow related to what is going on here.
File name for that version is PlexMediaServer-1.18.1.2019-c186313fe-x86.exe if you need to rebuild the URL for a download.