Apple Watch Series 3 update 8.7.1 bricked my watch

I noticed something weird with my watch:

before trying to update watch I updated iPhone to iOS 15.7 and after that my watch being on charger started to randomly reboot itself every 5-20 minutes but once I cut the connection with iPhone - it remains to stay on charging normally. When I connect iPhone back - watch starts random reboots again. Also when it's not on charging - it doesn't do reboots. Same thing was happening during update. I did it as Apple recommends - leaving watch on charger, but in that case it was constantly rebooting during transferring file causing interruptions and resumes. Once I figured it out - I no more doing update on charger.

Here is the tip for all of you: the fastest and safest way to update is to make it with watch itself fully charged (to 100%), connected to WiFi and not on a charger (maybe better even to disconnect from iPhone, but not unpair). For me it took 5-6 min to download update on a watch directly from internet. To do so you need the watch to be on watchOS 6+, paired (set up), connected to WiFi. But if you did reset your watch then before starting pairing make sure your iPhone connected to 2.4 GHz WiFi (watch don't support 5 GHz) then it will pass WiFi settings to watch and it will do download directly from internet as well (or maybe transfer by WiFi local network). Previously I did it using iPhone on 5GHz WiFi and it took me 2-3 hours because it was transferring 1.3 GB update file from iPhone to watch using Bluetooth.