Knapsu Plex Media Player Flatpak Won't Start

[Confabulated]

I'm in a bit over my head and hope you can help.

I have done a fresh install of Mint Cinnamon 20.1 and installed Plex Media Player Flatpak from https://knapsu.eu/plex/, a program I have always found to be extremely reliable until now. The program installs and opens from the panel icon for the initial screen for registering with Plex so you can access the local Plex Media Server, however, all subsequent attempts to open it result in it's surrounding frame showing up briefly and it shutting down. This also happens when trying to start it from the terminal.

I have been looking online for suggestions and the only useful thing I found was to input "unset SESSION_MANGER" before the "flatpak run..." command. This worked, it started fine, then it didn't subsequently work, the same behaviour (frame flashes up then nothing) returned.

I have tried installing the previous version of the program, fresh installs of Mint Cinnamon 19.3 and 20 (nothing fixed it), installing it on a VirtualBox Mint Cinnamon 20.1 - it works fine in that.

Any thoughts appreciated.

[Hoser Rob]

Have you tried the appimage version (you have to make them executable)? That link recommends you try it first.

[Confabulated]

Hi Rob, thanks for the reply. Yes, I tried that too, I should have mentioned it. Different results but still a fail. It would start but when I browsed to a library the frame stayed but the middle went grey and stayed that way.

I wonder if it might be something in the BIOS or something specific to this PC as the same setup works flawlessly on my old Dell 760 SFF and my Dell E5550 Laptop.

[Confabulated]

And the plot thickens, I went out for a couple of hours and when I clicked the start menu shortcut the program started perfectly. I closed it and it then it was back to the same issue.