I've had a long standing issue which has taken place across many releases and across multiple Hubs. For a while I thought this was caused by a problem in my network and with other things that had greater priority I havent done much to try to fix it.
One thing I noticed today was that both the web interface and Home Assistant can operate the AVR with no issues. This points towards a more Hubitat problem rather than a LAN one?
I don't pretend to understand this at all. But, does your Denon use telnet commands for control? Mike Maxwell is helping me get my Russound integrated into HE. Since upgrading to C8 Pro, I have frequent disconnects with my current setup that USED to work most of the time (with the C8). I suspect a telnet problem or something similar. Mike thinks something else. Just thinking out loud here.
@user4286 I haven't used the Home Assistant integration but do you know if it leverages a Telnet integration? If yes there is your problem. Denon and Marantz receivers only allow a single telnet connection at a time unlike other brands - My son's Onkyo allows 6 I believe for example. So if your HA is communicating with it via telnet that would prevent HE from connecting and vice versa.
My advice would choose one and then expose that device to the other if you really need to control it from both automation platforms.
To test this unplug your Denon receiver from the wall for 30 seconds and plug back in. Now go to your HE device and click initialize and it should now connect since the HA connection is now broken. Then you will likely get connection errors in HA.
