Smart radiator thermostat keeps recalibrating itself

I have 5 Tado smart radiator thermostats which I recently purchased. All of the radiator thermostats are working fantastically except for one. It keeps recalibrating itself. Oddly enough this one thermostat was in our bedroom and I would awake in the early hours of the morning to our room being 27 degrees. The thermostat would keep recalibrating itself and during this time the valve is open all the way which is why the room gets so hot.

Things I have tried.

Tightening the thermostat onto the radiator.

Tried recalibrating the thermostat.

Replaced the batteries and recalibrated.

I switch the thermostat with a thermostat from another room thinking it could be the pin on the radiator. I recalibrated both thermostats before moving them to new radiators. The issue still persists with the same thermostat.

I took the thermostat off and left it on my desk upside down and it keeps making an noise and displaying HI on the display (Not sure if this is normal behaviour).

I do not see any error messages on the thermostat.

By recalibrating I mean it displays the spanner icon and then the three squares run along the display. Then once it is calibrated it shows the three squares and then the set temperature with the hand icon.

Could this be a faulty device?