inconsistent / low heart rate readings

I have been using the Apple watch for the past few weeks now and I have been noticing some unusually low heart readings which I believe to be an inconsistency rather than a true reading. The readings will sometimes show 80bpm and in the same minute, it will show somewhere in the 40's and then straight back to 80bpm. They don't happen very often but they are showing on my dashboard as my minimum which makes finding my real minimum HR rather tedious as I first have to go and delete the low reading.

I was using the watch during a yoga session and noticed that the HR was rather low for a period of time - when I noticed it, I was in a static position with my arms completely straight so I took my own pulse and my HR was in fact about 100 bpm when the watch was reading between 40 and 50. It took a minute and the watch HR returned to normal but this is causing my average HR for the session to be lower than it should be.

I dont have any tattoos or anything which might interfere with the contact and I wear the watch snuggly throughout the day, but tighten it when starting a workout. I was wondering if anyone else has come across this issue and has figured out a way to resolve this?

42mm Space Grey Sport