Okay, so I found my old watch after 2years. iPhone 12Pro with Apple Watch Series 3. With 2.4GHz Wifi the download just started, but everytime the watch just rebooting randomly while the download is in progress. Tried to do the download on my arm. It is working. It is download the OS without any reboots but after the download finished the watch do a reboot then drop an error message that the Watch is not connected to the iPhone anymore. The iPhone shows Preparing... status. Anyone has the same issue? Any solution?