Altitude jump from 411 to 438 in 5 minutes during night.

If it happens during the night, could it just be the nightly auto calibration kicking in?

I don't know. But it has no GPS signal during night . isn't it essential for auto calibration?

In the nightly altitude calibration, the watch asks the phone app to provide location information, and then calibrates the altitude using the watch's DEM map.

Oh, it is interesting information, really, thank you. But my phone is disconnected during the night 

Many posts on this forum suggest that it also happens nightly with no phone connection. I have no idea where it gets the position information then (maybe it tried gps also, which might give a position indoors also, no idea).

So I am not the only one? Should I let it be, or should I try to replace my watch, or something?

Hi! Also similar night calibration would most likely make my altitude inaccurate, because I sleep in 4th floor  :-/