Has anyone else seen this issue on Pebble Time 2 with official firmware 4.36.2?
When I start a Run workout, the heart rate is initially accurate and matches another HR monitor. After roughly 20 minutes, the Pebble HR suddenly drops to around 77–82 bpm and then stays in that range for a very long time, even though my actual HR is around 140–150 bpm.
It does not look completely frozen because the value still changes slightly, for example 77 → 80 → 82, but it is clearly wrong.
Things I have already tried:
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tighter and looser strap — no difference
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stopping running — HR still stays around 80
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stopping and restarting the workout — sometimes it still stays around 80 and only recovers much later
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comparing with another HR monitor — the other sensor continues to show the expected 140–150 bpm
The interesting part is that I did not have this problem during summer. It started appearing when outdoor temperatures dropped to around 10°C.
Has anyone seen similar behavior, especially in colder weather? Could this be related to the Goodix HR algorithm losing the PPG signal and getting stuck on a low-but-plausible value instead of reporting invalid data?