I didn't think to check the temperature. I just saw it was going to be dry. Took me ages to warm up once I was home. Was all fun and games until my friend got a puncture and sitting around for 10 minutes took all the heat out of us.
So, I think what happened was we stopped for a coffee for about 25-30minutes. My guess is the strap went to sleep or maybe got itself locked. Wish there was a button you could tap on the device to reconnect or something. As I only noticed it stopped tracking 20 minutes later. Was going up a big hill and it seemed like hitting my chest didn't wake it back up and I had a few layers on so was difficult trying to disconnect and reconnect the device.
It was the magene arm strap I was looking at
@Martynt74 but maybe the Wahoo arm band one would be better.