I have been flying the H920 for 5 years now.
Partly I flew it in 800 km distance and never have I calibrated the compass.
You're talking about the yellow / orange LED that flashes?
As long as this only happens on the ground when you are above it, that is normal.
If it happens during flight, please provide us with the FlightLogs.
If it's only a few tenths of a second there, it's also negligible.
Please give us more detailed information.
Best regards from Switzerland,
Enrico