After spending several hours troubleshooting my network after the Channels DVR service suddenly stopped working from my Apple TV, I discovered that eero's "Advanced Security" was the culprit.
I sent this email to eero support, but I have yet to hear back:
"I use the Channels DVR Server application (https://getchannels.com/) running on a Mac Mini on my network in conjunction with the Channels DVR app on my Apple TV to watch, and record, OTA channels in my area.
After several hours of troubleshooting my network, I finally was able to determine that eero Plus flagged my Mac Mini running the Channels DVR Server as hosting malware, thus preventing the Channels DVR app on my Apple TV from working!
I have had to turn off “Advanced Security” in order to use the Channels DVR service again.
As a clarification, this traffic is on my local network only. Accessing the Channels DVR service via the internet with a port forwarding rule in place, poses no issues!"