My thermostat has gone crazy

Since a couple of weeks my thermostat has been behaving erratically.

1) It randomly shows temperatures jumping to 30C (see graph below) where the thermostat is sitting on a cupboard and is not exposed to any source of it (in the 12 months I have used before it never did that, and it was in the same exact location - definitely the local air temperature is not affected by any external factor).

2) the thermostat continues disconnecting from the WiFi network even if the preceding 1 year the connection was always stable. Nothing has changed in my WiFi setup.

Can anyone advise? Can this be a firmware related issue?

Thanks,

Andrea