Sounds like you’re facing and issue with The recent hub firmware update
which has caused communication issues with some thermostats. First make
sure that the hub is able to communicate with the thermostat. Open your
thermostat page try to turn your fan on and off. If that isn’t working then
you’ll need to fix that first. The best way would be exclude the thermostat
and then pair it again.
If it’s scheduled then the app is working the issue is the hub and
thermostat aren’t communicating likely. This was also documented on another
forum page.