HR not accurate after 16.19 update

1. Yep. It takes about 8 min for me, although I don't know if it's the update or the colder weather. 

could be weather, but I train in LA and Vegas, not so cold over here :)

Something really odd is going on with mine after 16.19 as well.  HR seems to display OK but i think its under reading in that my "base" pace for same HR is 30sec/km better (not likely) since the update BUT on the training load calculations its using a higher value as my base runs are tempo etc.

Theres something very wrong here.

My HR measurements are off as well, sometimes adding ~20 bpm to my actual heart rate during general use and sometimes all of a sudden going up to a HR of 180 during an easy run at the same pace during which I had a HR of 127 only minutes before. I have reset my watch to factory settings but now my VO2 max has dropped from 58 to 40 while my actual fitness is improving noticeably for the past weeks/months..

Did some more testing and its absolutely erratic and miles off.

General use im seeing erratic movements.

My max HR during exercise is consistently 186 and has been for a good while.  Last few attempts with this firmware and its auto updated to 196 even though the logs show nothing of the sort (base run- max 152).

I did a test yesterday and ran at what i know is my base PACE.  The HR displayed was about 12-15bpm lower than it should be.  Almost all of the run on the watch was in zone 1 and execution score of 10% *BUT* the performance calculations after it showed it as a good solid, high scoring base run.
This contrasts with the run at zone 2 with 94% execution score which is tempo.

To me it seems like there are 2 HR readings - the inaccurate one it uses for display and an accurate one which isnt shown in logs that is used for training calculations.

And yep, due to this VO2 Max, predictions, fitness age and all related metrics are going to be so inaccurate they're absolutely worthless.

First run this a.m. with new 255.  7 miles on treadmill.  Treadmill graph shows 150bpm +/- for about half the run then dropped straight down to around 120bpm for second half.  For an average of 138, should have been 150+.  And it calculated calorie burn of 634, should have been around 950.  (180 lb male, 9:30 pace, 66 minutes).

FWIW it seems an issue in other watches too:

High Heart Rate - Forerunner 955 Series - Running/Multisport - Garmin Forums

Guessing same sensor package and firmware, same bug.

FWIW this issue persists in 17.24.  Even after a full data wipe reset.