So the issue appears to be not specific to the touch display plugin as it occurs also when using the web interface on a third device.
In the meantime I have set up to Volumio systems (x86) as virtual machines. They show the same behaviour you described. That also argues for the issue not being related to the plugin.
To me it seems there could be a problem with multi room switching between devices. Might be related to the issues reported in the past, e.g.
https://community.volumio.com/t/multi-room-interface-switching/8269
https://community.volumio.com/t/multi-room-problems/8797/16
Maybe bring the issue to attention with a new thread describing the problem with turning off a Volumio system by using the multi room function.
What you could try for the time being is to connect a physical keyboard to your Pi and reload the interface by hitting F5.