ELEVATION ISSUE (again)

My Garmin gets the altitude completely wrong; look at these two images, on the left the 1050 at 10:27 am marks 544 m above sea level, an Edge 540 marks 543 m; at 6:31 pm, the 1050 marks 581 m, the 540 remains stuck at 543 m; the Garmin has already given me this problem, and it has already been replaced.