I have noticed strange behaviour of my Edge 530. When I start a trip the elevation value is sometimes e.g. 4000 m or 2000 m 
The correct value is 220 m. When I turn off and on the device it displays 220 m as it should do. The device is clean - I read about plugged holes of the pressure sensor. I have set manually the 220 m altitude for my "home" position. So I think it is a firmware issue. Now I use the 9.10 version as the latest 9.50 caused unexpected restarts of the device during a ride.