Hello,
As part of my Tri training, I started doing some bike-run brick workouts in August. I created a copy of the Triathlon workout and edited to remove the swim portion and renamed it Brick.
On August 7, my 955 had v11.12 and my HRM Pro was v8.8. I also use Garmin Rally RS200 v4.0. Everything looked normal/as expected on the bike portion. However, on the run portion, the run power was fluctuating between ~150 and ~1500 watts. https://connect.garmin.com/modern/activity/9358338776/3
The power for a standalone run 2 days later (and all stand alone runs since) looks normal https://connect.garmin.com/modern/activity/9369843055
I contacted Garmin Support and they had me restart the watch, remove and re-add the HRM Pro and then asked me to try it again.
On my August 14 Brick, the run power did the same thing again, but this time the 955 lost connection with the HRM Pro totally about half way through the run. Garmin Support concluded that the HRM Pro must be bad and they would send a replacement.
I did 3 more bricks, a mini mock Tri and a full Ironman using the HRM Pro and every single one had the run power fluctuating greatly.
After my Ironman I received a HRM Pro+ as a replacement. I had to wait until I was recovered before I could test it, but it too produces the same problems with the Run Power. By this time, my 955 was on v12.23 https://connect.garmin.com/modern/activity/9535573832/3
Today I decided to test further with my HRM Run (Black pod) and HRM Run (red pod) and the problem persists through 4 different HRM Run straps. I think its pretty safe to conclude the problem is not with the HRM Run(s)
I did a little more testing removing my power meter (same result), and then I removed all other sensors and accessories from the 955 and restarted the watch. Every time the large fluctuations occur in the run power.
I have reached back out to Garmin Support and I am awaiting a response. I fear they will ask me to factory reset my 955 
Posting here to see if anyone else is having this problem.
Thanks
Dan
