Apologies if a duplicate but forum keeps ignoring my posts which I’m trying not to take personally 8)
Giles, so this is the way it is meant to work:
1) at start-up, the App chooses the units based on the settings in your browser
2) then when it has connected to your OS device, it looks at the location you have set in the Map and updates based on that information
So, it could be that it goes to Fahrenheit first as your browser reports, say, “US”, but then later it sees that your Map selection is somewhere in France and changes to Celsius.
Does this happen from both the phone App as well as a browser on your PC. If so then let me know the browser you use as we can try and diagnose the problem.