Are you updated to the latest version of the firmware on your HDHR Extend? I’m showing 20190621 as the latest version available. It may also be worth it to open a ticket with Silicon Dust. I think they can use the codes in the Extend logs to see what is causing the application watchdog to initiate a restart, so post the first few lines of an example watchdog restart.
I read a thread recently where an Extend user had to manually power down their Extend and restart it after a firmware upgrade caused some problems… they said Silicon Dust told him to do that because not everything had fully restarted after the firmware upgrade.
On the Plex side, after the show has been recorded you can have Plex create optimized versions that are smaller using the Plex transcoder. I don’t do this since my Extend is transcoding ok (knock on wood), but I found a thread that might help where people are discussing it. Make sure you backup your originals when testing whatever process you use, at least until you know the process works…