Thermostat temperature setting

I have properly installed my thermostat, took less than 10min! Great videos on that. But then, not much of a user manual. It’s supposed to be intuitive and easy but I’m having issues setting the temperature. For example: I set my range to be 70 minimum and to start cooking at 80. I’m in FL by the way. And yes, I’d like the heater to go on at 70. However, often I’ll look at the thermostat and it says 68… the heat didn’t go on at 70. So I open the app and see that my temperature range has been reset by itself?!
I have it in the auto setting.
I find that I’m constantly having to go on the app to turn on my heater myself when I notice it’s too cold in the house.
What am I doing wrong on the settings?