Is it new? Has it always done this? Have you used any additional wiring harness included? Am not an expert but want to try to help. I experienced this years ago after installing an Ecobee without the additional wiring harness which provides power for the ecobee to run correctly. Each time the furnace would change states the ecobee would reboot. Never happened when using the AC. Something about a “c wire” missing from older houses and needing the additional wiring kit.