I used the MQTT HomeAssistant plugin to send a MQTT command from HomeAssistant to OctoPrint to establish the connection to the printer. Since the Octoprint Update to 1.9.0 this command is ignored/ misunderstood:
I just created a fork and patched the changes described in this issue. Install by copying/pasting the URL below into Plugin Manager > Get More > ...from URL and click install.
That's good to hear. I actually took out the OctoPrint version compatibility checks as it seems this may not be the reason it wasn't working. I've also downgrade OctoPrint to 1.8.7 and the patched version still works, so this must be related to a change on the HA side.
Yeah, I tested later the older OctoPrint version with the original and it definitely was working. I ended up adjusting my patch/PR to adjust based on OctoPrint version >=1.9.0 to use True/False, otherwise use on/off like before. Just needs to be merged and released by gruvin at this point.