I'm having a similar issue. My channels server machine crashed so I moved to a new machine. Channels finds all my sources except it is not finding HD Homerun tuner. I've tried rescanning network. The HD Homerun software is installed and runs fine.
What are you running Channels DVR on?
Is it in a Docker Container or VM?
Are your Channels DVR Server and the HDHR connected to the same ethernet switch?
Can you say what IP addresses your server and hdhr have?
Since we're not there looking over your shoulder, we don't know these things.
Great catch! I was on the wrong subnet! switched it to same and voila!! Thanks