Problem solved. Evidently there was something corrupted that was resolved by reinstalling everything including OS (revert to Xubuntu 18.04). I suspect a memory failure so I replaced one of the memory modules. So far that seems to have resolved the problem (knock on wood).

HDHomerun Config still crashes immediately upon startup. I've tried everything I can think of even to the point of completely erasing the system drive and reinstalling everything, including the OS (Ubuntu 20.04) from scratch.
Any and all suggestions welcome.

The HDHomeruns are plugged directly into PC LAN ports on the motherboard so I doubt the network path has been saturated.
It never gets to playing a channel. Any attempt to watch TV produces the all tuners are busy error.

Can someone please help? I've tried everything I know (not very much) and have gotten nowhere.

Thank you very much. I don't mind the blinking LEDs as long as it doesn't indicate some other failure.

I know the blinking green is supposed to mean problems getting an IP address. In this case the HDHR3s are plugged directly into the PC motherboard (ports ENP4S0 and ENP5SO respectively) and when I run hdhomerun_config discover both units are reported as: hdhomerun device 1323BF1D found at 169.254.21...

The leftmost LED on each of my HDHR3s blinks even when plugged directly into the PC.
When I run hdhomerun_config discover it shows both HDHRs with their 169.254.x.x addresses.
If the HDHR3s have good IP addresses in the 169.254.x.x range why should the leftmost LED blink?

I neglected to mention in my first post: The system is running Ubuntu 20.04 on AMD FX-8350.

I attempt to launch HDHomerun Config and it starts perfectly. However, after a couple of seconds I get the message: ERROR: communication error. At that point that window no longer functions. It will not accept keyboard or mouse input and the error message cannot be removed from the display short of ...

After I create the file 'unofficial-hdhomerun-dvr-repo.list' in /etc/apt/sources.list.d containing 'deb https://unofficial-hdhomerun-dvr-repo.s3.us-east-1.amazonaws.com/deb stable non-free' and run sudo apt-get update, I see this: E: The repository 'https://unofficial-hdhomerun-dvr-repo.s3.us-east-1...