Side button friends causes reboot. Replacement unit doing same thing.

You may try deleting the contact and make them again new. My bosses watch would crash on my contact and after deleting it and setting up a new one it works fine. He had about five contacts that would do that and the others were fine for some reason.

yeah, MacistheMac is right. The issue was never your watch. too bad they wasted a replacement unit on you with such short supply. It's got to be a software corruption on your phone. Try removing and re-adding the contacts there, but if that doesn't work go for a Settings > General > Reset >Reset all Settings. It won't erase your content but will forget some preferences and pairings with networks or your watch. If that doesn't work make an iCloud backup and choose Settings > General > Reset >Erase All Content and Settings. This will erase the content and preferences and when it reboots you can restore from iCloud backup and repair your watch.

Go to this thread where they have solutions for your issue. I can send Digital Touch, but can't receive. Any ideas?