Elevation profile in navigation activity is totally random

What have you set for auto calibration (continuous/at start or off)? But I think you haven’t started the activity...

I set continuous, but yes, I haven't started the activity yet... However, even if I start it, elevation profile remains the same, and why sometimes elevation profile is like first picture and sometimes like second one? I have done the same thing some minutes later from the same position...

Just tried now with "at start" and "off", but same result....

Same issue also with 4.64

and i don't understand also why if i'm starting from 107m the graph report 110m, but sometimes also 120m, 130m.... it gives me random numbers...

How flat is the terrain where you start?

If you are in a hilly location where a small GPS 2D error could place you in a spot with another map elevation, that would perhaps explain what you are seeing.

I'm seeing the same issues with my Fenix 5 plus.
I have near 100 activities for this watch both in the French Alpes as on flat grounds at sealevel.
Using the manual calibrate with DEM always gives a good result.
However it seems this watch isn't using the DEM files at all during an activity (independent of the auto calibration settings)
It ALWAYS seems to use the GPS height which can be very far off (20-30m is totally normal (for this watch and others))

During (almost) every (flat) swim i calibrated the Watch before each swim using DEM which gave the right value.
If i use auto calibration (continuous or at start) the value after the swim was always very different than the calibrated value before the swim (gps track is good).
Indicating the unit always uses the GPS height and ignores the DEM values.
Doing the same DEM calibration after the swim reports the right value again.
Swim is the easiest to test as there is no height difference during a lake swim.

During a running activity i see exact the same however there is always some up and down movement.
When doing no calibration at all the Garmin seems to ignore the DEM info and always uses the GPS height.

Even various times on the bike the incline (based on height) is totally off ( indicating 0% for minutes while reality it is continuous 6-12%. Tested during multiple 1 hour+ climbs)

The Fenix 5 plus and reliable height measurement are two opposites.

I'm seeing the same issues with my Fenix 5 plus.
I have near 100 activities for this watch both in the French Alpes as on flat grounds at sealevel.
Using the manual calibrate with DEM always gives a good result.
However it seems this watch isn't using the DEM files at all during an activity (independent of the auto calibration settings)
It ALWAYS seems to use the GPS height which can be very far off (20-30m is totally normal (for this watch and others))

During (almost) every (flat) swim i calibrated the Watch before each swim using DEM which gave the right value.
If i use auto calibration (continuous or at start) the value after the swim was always very different than the calibrated value before the swim (gps track is good).
Indicating the unit always uses the GPS height and ignores the DEM values.
Doing the same DEM calibration after the swim reports the right value again.
Swim is the easiest to test as there is no height difference during a lake swim.

During a running activity i see exact the same however there is always some up and down movement.
When doing no calibration at all the Garmin seems to ignore the DEM info and always uses the GPS height.

Even various times on the bike the incline (based on height) is totally off ( indicating 0% for minutes while reality it is continuous 6-12%. Tested during multiple 1 hour+ climbs)

The Fenix 5 plus and reliable height measurement are two opposites.

Report it to beta team!