I was facing the same auto restart issue on my M51 previously. I did these 2 things.
I uninstalled updates of Android system webview ( please note I haven't disabled it) And secondly I updated Play Store from apk mirror, which brought back the Google Play System Update button in the settings. There I checked for update and it said to restart in order to apply the update.
That's it. My M51 has not auto restarted since a week. I don't know which of these 2 worked. But It's okay now. Sometimes in this week if I felt any lag, I cleared recent apps or clicked the optimize button in device care.
We acknowledge your query and apologize for the inconvenience caused to you and will surely assist you regarding the same and please follow the easy troubleshooting steps which might help to solve the issue.
There are two methods to disable the auto-restart function Method 1: From the home screen swipe up or down to access the App Screen > Setting > General Management > Reset > Auto Restart > To Turn OFF auto-restart slide the slider toward the left. Method 2: Go to 'Settings'>>Tap on 'Battery and device care'>> Tap on Three dots>>Tap on 'Automation'>>Disable 'Auto-restart at set times' if enabled
If you are facing this issue after installing any new application then uninstall that application. Navigate to the Apps screen and tap on Settings>>Tap on Apps>>Tap on the desired app>>Tap on Uninstall>>Tap on OK
Reset settings: From the home screen, click on Settings>>General Management>> click on reset and then reset setting.
If the issue still persists we would request you to kindly visit your nearby service center, for the physical inspection of your device. Please be assured, our team will surely help you with this.
