So for closure - or progress in case anyone else ever experiences this - I have decided to bypass the problem by buying a Pegasus Powerbox Gen 2 - which as well as providing controlled USB and Dew heater ports - it has a high quality temperature / humidity and dew point guage.
Luckily APT gives Observatory monitors - of which it classes the Pegasus - as a higher precedence source of truth to the ZWO mis-behaving thermometer.
So in a week or two I hope the weather improves and my focusing returns to top notch!
https://bintel.com.au/products/pegas...2?gad_source=1