Marantz/Denon binding in OH3 - "IO error while connecting to AVR: java.util.concurrent.TimeoutException: Total timeout 5000 ms elapsed"

Tags: #<Tag:0x00007f173b4d9640>

I have a Marantz NR1506 AVR that worked just fine with OH2, using HTTP control.

But since upgrading to OH3 I can’t turn the AVR on from OpenHab. The Thing shows as Offline with:

COMMUNICATION_ERROR

IO error while connecting to AVR: java.util.concurrent.TimeoutException: Total timeout 5000 ms elapsed

shown at the head of the page. The AVR is enabled for Network Control always, and I can still ping and use the built-in web control. So it’s definitely still accessible.

What gives?