Here is what I did last week Wednesday evening that so far has been helpful.
- On the iPhone app Watch - Notifications: Disable the Notifications Indicator and under MIRROR IPHONE ALERTS FROM:, change all notification sliders to the left (Off). (Did not change any of the factory apps, left them at Default after a recent pair as a New Watch attempt.)
- Restart both the iPhone, and then the watch. I had read about others thinking that this was related to Notifications and some mentioned Instagram (which I had also removed before starting any of this without any changes). I observed this for a couple of hours while working and at this point it was rebooting every view minutes or so while connected to the charger. I removed it from the charger and it still continued to reboot many time. It was time to try one more time as I had an appointment at the Apple Store to drop it off and ship it to be looked at.
- On the iPhone app Watch, select the watch to be unpaired from the iPhone and un-pair from the iPhone. Wait for it to un-pair before continuing.
- On the watch it will be prompting to place near a phone to be paired, forced a local reset on the Watch by pressing the Side Button and acknowledging to reset all. (Do not remember the exact wording or clicks, it does not allow anything else to be done though since it is not paired to a iPhone.)
- Once the watch is ready to pair again, placed it next to the iPhone and then paired it again. I followed the normal pairing of the watch and restored the recent backup (right before I started the process) to restore all the settings. (I was a little hesitant, although I figured I did not have anything to lose.)
- After it has finished pairing and was running, the battery was at about 82%, it had been rebooting several times before I started this process and was done at about 9:30-10:00pm.
After this process, I wore it to bed and when I got up it was still at about 60% or more. I wore it until about noon I decided to charge it while at 31%. It was fully charged in about an hour and I put it back on. It did not reboot once all day, and worked normally with minimal battery drain. The next morning the battery was at about 30% when I charged it at about 8:30am.
It has been like this since Thursday morning with not one reboot and also has not been draining. On Saturday night, I re-enabled the Notifications Indicator, I am planning to start enabling notifications to see if anything causes a problem. Yesterday I did not get to place it on a full charge before leaving in at 6:15am, it was at about 90% and it was a very active day. At about 11:00pm last night is was at 17%, placed it on the charger for about 30 minutes or so, it was at about 91% when I took it off to wear it to bed. Got up at 6am and it is still at 80% at 8:30am. Not one issue since doing all of this.
I plan to start enabling the notifications that I might use and leave the others off. I also have not reinstalled Instagram yet. I might do that first to see what it does.
I hope that someone else might try this (I know it takes time, although if it works or helps Apple to find a root cause it is worth it) and see a similar result. I have been dealing with this since updating the middle of December to WatchOS 4.2. I am 100% sure that it is some software thing (I work in software and root cause analysis all the time), although it not widespread, it has to be some certain combination or scenario that causes it to happen.
