Tado resuming schedule at midnight

Since the start of Spring, I’ve had my thermostats set to off (frost protection). I’ve done this with the slider in the app and set it to stay off until I resume schedule. The upstairs thermostat seems to have a mind of its own - staying off for days but then randomly resuming schedule at midnight. The heating then kicks on at 5am - while we have a window open no less. I’m going to set the system to ‘away’ permanently to hopefully stop this happening again.

With the cost of energy these days, this is absolutely infuriating. Tado is costing us money with what seems to be a software bug.

Is anyone else experiencing this issue? Any ideas about how to resolve it?