Have you received any resolution? Your example shows that there is something and it has to be software and related to the interaction with the iPhone, as not everyone is seeing this. I updated yesterday to the new WatchOS and starting last night I could not stop it from rebooting and drained the battery in a couple of hours. Today while on the charger, it was constantly rebooting about every 5 minutes.
I am about to send it back to Apple through a store on Friday. I am 99.998% sure that it is not a hardware issue. Interesting that as soon as I un-paired it from my iPhone a short time ago, it has not rebooted since. It is is just waiting for me to connect to a phone. The reboot is happening while paired. I did not think about shutting off the phone to see if it stops. Experiment for later tonight after re-pairing (again).
So frustrated with this, can't imagine yours with getting a new one and problem still existing.