This comes and goes with different versions of the software version on the Fenix 3 but it's clear that the problem lies with GC.
We have to edit each activity manually to turn off Elevation "Correction" to show correct data.
VERY ANNOYING since this is supposed to be a trail watch.
It seems like a trivial thing to fix, when the problem first showed up it was fixed quickly but only for certain software versions for this watch.
Example:
https://connect.garmin.com/modern/activity/1069289717
Unit ID: 3906483619
Software: 6.84