Ah I see, Rob 
Well, I use (advanced) virtual devices to disable flows, it works fine (not what you want to hear right now 
).
Here’s what I use
The advanced virtual device on Homey (but should work with Homey virtual plug, or virtual devices app as well):
As published with MQTT Hub & MQTT Client:
It’s added to HA as MQTT device:
And can be used as automation trigger:
Wherever I push this virtual sensor OnOff switch, it’s turned on or off on both platforms.
I suspect something going on with your MQTT Hub settings.
Just to make sure, did you use the custom settings, as shown in the turorial?
The default settings left me with un-synchronised MQTT devices on both platforms.
