Hello, try to compare those two courses: one rider with 830 (my friend):
https://connect.garmin.com/modern/activity/9447860631
the other rider with edge 1040 solar (me):
https://connect.garmin.com/modern/activity/9448077971
the ascent profiles are completely different. The one recorded with 1040 is correct! so the 830 is wrong; the strange thing is that my friend's 830 ha been changed, by garmin assistance, 3 times so is the thied device with the same problem, ascent completely wrong.
the strange thing is that each device run well for the first months, then is starts to have strange beeaviur.
I don't kwow why it happends.
tsk Marco