@valdek44g @A1mark
Check the following suggestions.
1. Modify the schedule to non-consecutive rules, leave a gap between two schedule entries where no settings are applied. Monitor whether the early start works in this case.
2. Recalibrate the KE100. Go to KE100 Device Settings page > choose Calibration.
3. Fully open the KE100, wait for a while then fully close it, and monitor how the temperature changes. Please share a screenshot of the report chart after this operation. Go to KE100 Device Settings page > Summer Mode > Enable Summer Mode, select Fully Closed or Fully Open.
@valdek44g Regarding the issue of the temperature not reaching the set value, are you referring to the temperature adjusted through early start? Would there be any issues if the temperature is adjusted manually within the Kasa app?
When you mentioned using the thermostat head can adjust the temperature correctly, does this refer to physically switching the KE100, or is it referring to thermostat heads from other brands (non-smart)?