Abnormal heart rate when doing "Cardio" workout Fenix 8

I have the latest version (not beta), when I start a workout on the elliptical, for the first 3-4 minutes my heart rate is 160-170. Then, after a while, my heart rate becomes normal, around 110-120. I even tried taking off the watch, wiping the sensor, moving the watch to the inside of my wrist - nothing helps.

F8AMOLED47

Mine still reads extremely high on its own without a strap.  I did a 45 minute strength training workout Friday it still shows I need around 35 hours to recover, three days later.  The stats show most of the hr in zones 4 and 5 when they never get that high when wearing a strap.  I try to use a strap but i don't always have it with me.  All my old Garmin and Apple watches have been decently close but the new Fenix8 is not even in the ballpark.

Hey, I recommend you connect up a strap and record both. Then you are comparing the same reading. I tested my Enduro 3 and it was a near perfect match with strap. And it was live, so recording at same time. 

Same experience with my Fenix 8 47mm. During warm up and 15 minutes in it can show 180 beats where 130 is the norm. Than the training indications are already messed up for that training. I stop and figit the watch around... It's already very snug on my wrist.... Wait a bit and it returns to a normal registration of the heart rate. So disappointed in Garmin and this extremely pricey watch. They fixed it on the Forerunner 945 where this was also for some time the case. So fix it for Fenix 8, Garmin!

When I walk in the gym, my heart rate is about 80. When I switch on "strength" it goes up to almost 160. While doing nothing more physically then before the button press. After about 10 minutes my heart-rate goes to normal levels. To me this is a pretty clear sign of a software problem, and not a sensor problem. Not exactly your issue, but I think it's related. (copy paste from another thread, but it seems on topic)

I don't record both separately but I do wear a strap most of the time because the watch is so far off.  When taking a walk during lunch at work without a strap the watch thinks I'm putting in much more effort than I actually am and suggest a long recover, for a casual walk on flat ground.  I'm a runner and did a max hr test to adjust my training zones and still didn't reach the max hr the watch will show at moderate levels of intensity.  Like others have stated, it's typically just the beginning of the workout but it throws off the effort and recovery calculations.  I don't solely rely on them but am disappointed it isn't more accurate.  I started with a Fenix 3 and have had other Garmin watches with great results, I just don't understand why this product is so bad.  I've been putting it off but plan to put in a warranty claim to see if they are willing to do something about it.  Obviously it works for others as most responses are to get checked out by a doctor because my hr is to high but I know it's the watch.  If it was me I think my heart would have exploded already based on what it reads at times.

I'm getting stable reproduction:
1. Start the Ellipse workout
2. Connect to HR Broadcst on the TechoGym machine
3. First 3 minutes heart rate 170 instead of 120
4. Then heart rate becomes normal.
At least it happens every second day. Version 12.38 fenix 8 47mm AMOLED

what doesn't help:
- Tried changing the location of the watch
- Moved the watch to the inside of my hand.
- Tightened my hand too much with the strap
- Didn't move my hands.
- Paused training