For God's sake Garmin, go back to the factory version of the 955.

I do have the 11.12 update in the form of a GPUPDATE.GSP file... but to be honest, no clue if you can downgrade (assume not) and not willing to try out either.

But there were sensor/whr updates from 9.12 to 10.10 and then from 11.12 to 12.23

11.12 was solid out of the box and my best Garmin experience for the last 10 years of ownership (FR225, FR620, FR630, Vivoactive 3 and FR645).  With the new updates 12.23 & 12.27, I'm back to ignoring my 955's suggestions and observations.  

Totaly agree!

Please give us a possibility to downgrade! I'm also experiencing issues with each update. 11.12. was good enough at least

This problem of falling or increasing heart rate in races is unfortunate. I had to fix this as soon as possible. It impacts all the watch's metrics and it is practically unusable.

I miss the 11.12 too.

Had accidentally upgraded to 12.23 when I was downloading files to send to Garmin.

A move that I regret. I shouldn't waste my time to send the data. In the end, Garmin Kevin closed my case because of not enough data. Truly absurd !

My suggestion is to invoke the warranty and get a replacement watch. And hope it is loaded with the 11.12 firmware.

DPSK said:

My suggestion is to invoke the warranty and get a replacement watch. And hope it is loaded with the 11.12 firmware.

I got file with firmware 11.12. Is there any way to downgrade with it somehow?

My despair that I have a marathon run now on 10/29 and I can't trust the clock. I'll have to use the crap that had already retired the apple watch. Detail today I discovered bug in pace and distance too.

I have not tried.

Would you like to try? 

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

Tanks.