Just to share mine and my girlfriend's "experience" today. We were on a 9th kilometer of 14 kilometer hike. We were both recording the activity as hike, using different data screens each of us had setup before. Both of us were using "navigation" based on previous activity we recorded a week ago (I was using my recording and she was using hers). so, suddenly her watch stopped responding - no reaction on button presses etc. I checked my watch and it was just slow when scrolling between data screens. 2 minutes later I had exact same problem. I was still getting "1 km distance alerts", but, nothing would change on the screen. When we finished the hike, we tried to soft-restart our watches, but they would just get stuck on Garmin logo. We had to do the hard reset at home, wiping our settings and killing the activity. So, activity lost, settings lost, another 30 min spent on re-configuring, re-pairing etc.
Wondering, what on earth can cause two watches freeze like that, never happened to us before!