I have an FR 255 and for the past two weeks the altimeter has not been working properly. It suddenly changes altitude and shows me that I am between -3000m and 8000m. The information shown on the altimeter graph is also inconsistent. I have turned it off and on and also calibrated it several times. When I calibrate it, it shows me the correct altitude, but if I accept the calibration, it goes back to the previous implausible altitude.
It is clear to me that it is a software problem and that the sensor is working properly. When I finish an activity and sync it with Strava and Wikloc, these apps show me the correct altitude and the activity graph is correct, but when I check it on Garmin or the Garmin Connect app, it does not show me the activity altitude graph.
What could be happening?