@Naseefnas: Please try heading to Settings > Device care > Auto optimisation > Auto restart, and make sure that this feature is toggled off. If it is, tap the Back button > Maintenance mode, and select 'Turn on'. This will disable all third party apps, and help to determine if the problem is stemming from an external source. If you lock your device while Maintenance mode is active, does the issue persist? If not, disable Maintenance mode via the drop down notification, or head back to Settings > Device care > Maintenance mode > Turn off, then uninstall any apps that you have added to the device since you first encountered the issue.
If Maintenance mode is not available, restart the phone in Safe mode for the same effect. To enter Safe mode, press and hold the Power button until the 'Power off' prompt appears on the screen then release > Touch and hold Power off until the 'Safe mode' prompt appears then release > To confirm, tap Safe mode.
If you find that the issue is not present in Safe mode, then please restart your Galaxy A31 as you would normally and uninstall any apps that you have added to the device since you first encountered the issue. It won't be possible to determine exactly which app is at fault, therefore we recommend approaching this via a process of elimination.
