An HF alert after a power outage isn’t telling you something is broken — it’s telling you the cabinet experienced a temperature rise while the power was out and giving you a heads-up to check on food safety once power returns. The unit itself typically resumes normal operation on its own once power is stable again.
What to actually do with that information depends on how long the power was out and what you find inside: look for signs of thawing or warming, and when in doubt about perishables, standard food-safety guidance is to err on the side of discarding rather than risking it. If HF keeps appearing without an actual outage having occurred, that’s worth mentioning to a technician, since it could point to an intermittent power-supply issue worth investigating.