Manged to fit a very very short MTB ride in yesterday, a ride with my boys to their Nans, then off road and messing about coming back. Seemed to run fine, and since they have not gone down.
I did spend a day with the wheel on its side, moving it about, turning it over etc. They are light weight clinchers, and perhaps not ideal for Tubeless, I expect the thin sidewalls may well be letting out air slowly - but hoping them being on their side for longer will help this.