WORKAROUND FOUND
So I finally found a relatively simple workaround, so long as you are familiar with sideloading apps. If not I will try and summarize.
Download the previous version of the Plex for Fire OS apk from here:
Plex for Android - #525 by PlexAndroidReleaser (Both Fire OS and Appstore apks are the same)
Direct link: https://downloads.plex.tv/Kepler/kepler-armeabi-v7a-amazon-10.26.0.2578-6cc7ea1a.apk
Uninstall the existing Plex version from the Fire TV device.
Under Settings → Applications → Turn Off Automatic Updates
Now for the sideloading:
Go to Settings → My Fire TV → Developer → Turn ADB debuggin ON (can turn off after the install)
Now if you are familiar with command line ADB you know what to do. If not then I recommend the following Android app to do the sideloading for you:
At this point Tap the connect icon in the top right, select your Fire TV, click Allow on the popup on the Fire TV itself and finally go to the Custom Apk tab in the app and select the file downloaded above.
I really hope this helps other people, it’s no where near a fix but if you, like I need the continuous play function this is how to get it back for now.
If the version I linked doesnt seem to work for your Fire OS device, try going back an update further with the following link, or find a version that works for you in the thread linked above.
Jan 6th Version: https://downloads.plex.tv/Kepler/kepler-armeabi-v7a-amazon-10.25.0.2457-6d4c0187.apk
