I use ForeRunner 745 and I noticed that for the past 2-3 weeks, unless I'm doing an absolutely flat run (along the beach), during each of the training sessions there is a moment when the altitude suddenly drops 30-100m and then it stays there and it's wrong so I have to recalibrate. I have Auto Calibration on and sensor is set to Auto.
I run with a friend who uses Fenix 6 with the identical settings and there are no problems with their device.
Is that normal? Expected? What should I try to fix it?