Hi, during my swim of around 50 mins where I cover 2.5 KM of distance (at a pace of 1:34 min / 100 mts), my heart rate remains only around 100 bpm. This has been a sudden drop. I understand that I could have developed good heart affinity but till 3 days back the avg. hrm was around 135 for the 1 hour swim with max touching around 150 range. How can there be a such as sudden drop. And because of this, the intensity minutes have dropped to 0 for the activity. There was an update that got downloaded today on my watch (its always auto update) but I am not sure what is wrong. The sensors are clean and no damage seen. Can you please guide me with resolving this issue? (Garmin Forerunner 745)