Experiencing the same issue with AirPods Pro 3. When no workout is running I see a heart rate sample every ~5 seconds in Health App on the heart rate page. When a workout is started f.e. through Apple Fitness the heartbeat sample is being received by the workout app. I can see the BPM updating inside the Dynamic Island while those samples are not being recorded in the Health App anymore and are also not queryable through HealthKit. Tested on iPhone 12 with iOS 27.0.1 and iPhone 15 Pro with iOS 27.2 Beta

Same for me, was trying to fix it since over 1 hour... Glad to hear that the issue is not on my side