Rebooting watch

Since the latest update, my watch keeps freezing and randomly rebooting.

The other day within an hour or so it dropped from 40% battery to 10% so I had to put it into power save mode for a couple of hours. I put it on the big charger overnight but it still would not exit power save mode the next morning. I then put it on a different charger for an hour on my commute it was still stuck in power save mode when I arrived! A bit later it randomly rebooted and reported 100% battery.

It keeps on freezing and rebooting so consequently all my activity recording is also back to square one!

Any ideas?