Even with the watch very tight the watch will drop my heart rate. After it recovers which can take minutes it is often very low. This is happening while doing a simple fast walking workout. Tonight it dropped out and when it came back it said my heart rate was 78. I have been using chest straps for a while and know when walking a 15 minute mile pace I should be in the 140's. After a few minutes it will catch up. My watch worked perfectly all summer then this started. Apple replaced the watch and now the new one is doing it. Also today in just doing a random check it said that my heart rate was 198 walking around a store.
Apple Watch Sport 42mm, iOS 8.4.1, Watch OS 1.01
