Noticed this outdoors first, where the distance stopped recording during an outdoor run. Stopped and started the activity again and seemed to work again.
Noticed again today during an indoor run, that several times during the hour, it just flat out stopped recording. Heart rate and time elapsed worked fine, looking at the activity after and the cadence showed the same as it was the rest of the time, and steps seemed to be counting, but the distance and pace didn't change. On one occasion during the activity there was 3 minutes before I realised it hadn't changed, and on looking at the activity in connect, this is very clear as the pace just drops to nothing for the full 3 minutes.