I have the native Ecobee integration and the Homekit integration setup. Occasionally I will get these spikes in temperature but only on the Homekit sensors. Obviously the room is not jumping to 212F suddenly. Is there a way to avoid this? I tried looking in Developer Tools → Statistics to remove it but nothing is there
Bumping, because I also have this problem as well, across two separate HA instances and 3 thermostats. The temperature plots I have from existing API integrations do not have this problem - only the local homekit integration.
Have you tried the Filter intergration ?
The sensor first reports 212.0 F before the actual reading when the thermostat restarts. In my case the thermostat restart was due to the automatic water feeder being activated and taking away the power from the thermostat wiring.