We have lots of power outages here. This causes our Shelly 3EMs to reboot and then HA records a major peak of 1000’s of kWh being consumed. Energy monitoring (at least in Europe) is top-prio and this is very annoying.
Is it the Shelly 3EM reporting this energy spike?
Check the emeters values at http://<shelly_ip_address>/status
If it is then that needs to be reported to Shelly.
If not, are you using a template to add up the three phases?
If so, you may need to add an availability template.