Altimeter problem after upgrade to 15.20 firmware

I found the problem out of the activity, then I didn't do any activity :-(. I contacted Garmin support in the Czech Republic yesterday, but I have not received any response yet. 

www8.garmin.com/.../download_details.jsp

www8.garmin.com/.../download_details.jsp

It's odd, I have the opposite experience. I have my 5 Plus and Fenix 1 set to 'calibrate altimeter at start', wore them during the same activities, and the Fenix 5 Plus had more accurate altitude since 15.20 than before, while the Fenix 1 drifted with the atmospheric pressure as it always does. Don't know why image looks so fuzzy, but you get the idea (Fenix 1 drifts from ~10 to ~ 80 meters).

If you haven't tried it yet, maybe it helps to change to 'calibrate at start'?

Thank you, but only 15.00 Beta to download ...

Don' t install 15.00 !  Inside backup folder there' s 14.00. Follow easy instructions

"

1. If you would like to revert to the last public release software, drop the gupdate.gcd file found in the System_Backdate_v14.00 folder in the \GARMIN directory."

Thank you, I don't have a cable with me now, I'll look at home.

After seeing my last two runs they simply told me to send the device to repair or replace. Then again I'm pretty sure it's a software issue, as 15.20 made it a lot worse :/