Recently I have started to experience really abnormal heart rates from my 945, i seem to have been able to pin point it to an exact day when it happened and just so happened I did 2 similar runs back to back and the more intense run had a lower heart rate:
This is what the heart rate looked like during the "intense" run and you can sort of see where the heart rate suddenly dropped off:
Every since that particular run, my indoor and outdoor cycling rides have been wonky as well with my HR refusing to go above 100bpm mostly when I know I should be around 150bpm based on effort and power.
An example, ridiculous my HR can drop to 58 while at constant 100+w effort:
Note this issue started on FW 2.70, i have updated to FW 2.80 and it does not appear to have fixed the issue but the only time it has registered proper HR vs my perceived effort is during OHR swims.
