For about two Weeks I noticed my Forerunner 955 simply stopped measuring HRV in the second half of the night continuously. There sometimes are small measurements and sometimes none at all. I mainly noticed it because my overall HRV Score went way down, as the higher values from the end of the night were missing. I know the HRV Measurements aren't the most accurate to begin with so I usually use them as a very rough guideline, but the score also affects other metrics like training readiness and the suggested workouts. As a result the bad readings are breaking some of my most used features. At first I thought it was because I was wearing the Watch too loosely on my wrist and the sensor didn't make contact, but even with a tighter strap setting the Problem remains. Rebooting the Watch also does not seem to make a difference. I have been on Sofware version 16.17 pretty much since its release, so the problem probably does not come from an update.
Below are the measured Curves where you really see the problem. 1 is a typical reading in the past weeks, 2 is a very extreme case and 3 is a normal reading from before this started. I don't think the Hardware suddenly stopped working, as everything else about the HR Sensor seems to work normally. The bad measurements have persisted long enough now to make me think there is something wrong with either the HRV Measuring itself or the watch thinks I am already awake after 2 AM, as I have had two or three weird sleep measurements as well. Either way both would appear to be software based, so I am wondering of anyone else has experienced this behaviour.
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