Floor climbed jumped 20 floors on a flat 12km run

From the activity details you linked, it looks like you had 236ft of elevation gain. I'm guessing they use ~10ft per floor, so +20 floors would be about right for that run.

Thanks renhoek54 , that would explain the floors to elevation correlation. The elevation gain of 236 ft however, is suspicious as this was a flat terrain around the lake. never mind, could be one off error. Does Garmin Instinct connect use the inbuilt altimeter for run elevations or rely on inferred calculation based on GPS coordinates ?

Hi @ajayvm.. If you zoom into your elevation plot, you'll see a few erroneous elevation spikes around minutes 48 and 50 that account for most of your gain.
I see this was on 2.80 firmware. For what it's worth, after I updated to 2.80 I started seeing a lot of bad barometer data like this. I rolled back to 2.60 and have yet to observe them again. I am suspicious that there is an issue with barometer in the 2.80 firmware, but haven't yet been able to convince the Garmin support techs I've been talking to via email.

I've had wild elevation tracking results with my Instinct, too. Elevation track would be fine for about 20-30 minutes, then start jumping up and down. On one 10 mile run, it doubled the actual ascent gained. I contacted Garmin Support, they exchanged my Instinct for a new one. Been on two runs now using the new watch and am having THE SAME ISSUES. Also noticing that the heart rate track also is very jumpy. I need to go back and see if it was happening before the move from 2.60 to 2.80. SO VERY FRUSTRATED.

Edited to add that I checked my data and the problem was appearing on the 2.60 as well as the 2.80 update.