I’ve just spun up a Docker container with MQTT and connected one Shelly to it. Restarting that instance does not turn off the light but it does with the Hassio MQTT add-on. I also had an issue with the Monitor presence detection where the two Pi’s I had would flood the MQTT add-on with connect/disconnect messages and essentially make all my MQTT devices unusable. It did not appear to behave the same with a Docker instance on my NAS.
I might try flicking everything back to my Docker instance and see how I go.