I would try 2 things first, before looking in to any possible hardware issues. First, find a place nearby in a WIDE OPEN area with nothing within 100 yards or so of you and do a compass calibration there. That way you should be able to eliminate any possible calibration errors that could have been introduced. Then try that same flight again. ( Or close to it ) and see if you get any messages. If not that should correct the issue. If you still get the errors, then try a cold IMU calibration. In the interim, you could pull the .dat file from the AC and place a link from a sharable location back here so we can view that file. It may or may not offer more clues as to what may be going on. If you have not done that before, see the link below.
How to retrieve a .DAT
How to retrieve a .DAT