Thermostat not updating

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Hi. For the past few months I’ve been having an issue with the thermostat not updating. My heating is set to come on each morning at 7:30am and set to 20 degrees. Most days this works fine. Every so often I notice the heating hasn’t come on and upon checking the app it says it has and it’s set to 20 degrees. The issue is the thermostat has not updated and is still set at 16 degrees for example. Changing it to 20 degrees on this will then make the heating come on.
As I say this doesn’t happen every day. Does anyone else have this issue? Is it a bug? Any idea how to resolve?