I am getting angry ???????? with the constant craziness in Elevation Data.
I run in flat park by the sea and it gets me several meters underwater and several meters flying!!!
PLEASE GARMIN LET US DISABLE ABC ALTOGETHER
I have had the same problem with two Garmin Devices.
The issue started with my Vivoactive 3 around October/Nov and last week, I replaced my Vivoactive 3 with FR645 and the issue has not disappeared. There is atleast 30% error in the altitude measurement.
I usually wait 30 seconds after the watch has acquired GPS in order to complete calibration. But this does not help.
As someone suggested, my next step would be to try to acclimatize the watch for 15 mins by not covering my watch with sleeves and start running only 15 mins after the watch is exposed to the outside air.
Garmin has to find a solution to this before people start moving to other watches.
What is really surprising is, all the people who review watches in detail in youtube and their blogs have not mentioned a word about this issue. Does it mean they are conveniently ignoring this because they are paid? or it is just that they don't have this issue in any of the Garmin watches that they have reviewed? It is really amusing that they don't have issues in the watches they review because almost everyone I have spoken to have complains about their Garmin on elevation issue.