No it's not, during my last Forest Bike trip, the trip was recordered with an elevation 500fts above the right one. (I haven't fly with it since the issue).
Nothing seen in front of the sensor port.
And finally it went back to normal 3 days after. It's the third time I suffer this issue...
I call Garmin support they told me it's related to hardware issue.
extract :
" I’m sorry to hear about the problems that you experience. We received similar reports from customers and completed full investigation with the engineering team. Sadly, resolving the altimeter issue proves very difficult as it is hard to reproduce that problem in the lab. The last time I heard back from engineering, they said that they suspect that static energy is affecting altimeter. This would explain why we receive increased number of complaints towards winter when the air is dry and people wear multiple layers of clothing. Bottom line is that we cannot count on software solution for this one, as the problems appears to be related to the hardware. "
My watch has been sent to the support team with an RMA.