I bought a Fenix 6X pro last month, and used it for a few weeks and everything seemed fine. I had to get it replaced since there was something funky with the watch since the back of the watch says "Sapphire" though I paid for a Fenix 6x Pro only and customer service confirmed that the serial number was also only a Fenix 6X pro.
After I replaced the watch, I started getting consistently low readings on my heart rate on all activities. I have tested it against past activities, tried rebooting, updating to 12.2, warming up, wearing it correctly, etc.. but both running and bike measurements are consistently lower, which leads to every other metric getting messed up. Calories burnt, training metrics and not to mention every single Strava training metric as well. In the example below the first ride had a strava relative effort of 186, but the second exact same ride (near identical time as well) shows only 42. These are 20 days apart, I coudnt have possibly improved my fitness level so much and dont think an professional would be able to climb a hill on a bike at 120 heart rate as well.
Here are the two rides on identical routes and identical speeds.
The first ride is with the first watch, which seems to make perfect sense with the up-hills and the physical exertion I felt on different parts of the ride. the second ride is from today on the new watch, which shows a much lower heart rate overall.
Here is a chart with both the rides stacked up.
They start off fine, but after the first hill climb, the heart rate is consistently lower. There are many parts where im sure it is wrong.
- The last 3km is definitely wrong since I was cycling relatively hard, but the heart rate is 110 on average, which seems very low.
- Even if the 110 was right, the 2nd hill climb averaged 120 (first ride is around 170). There is no way I climbed the hill with 120 heart rate vs 110 on a flat road!
- Apart from the first hill climb, the average heart rate on today's ride was around 115, which is what you expect from a brisk walk. but this was a strenuous exercise. The first ride averaged 160, which is more realistic.
