That's not what should be happening @Anjan Kumar
A factory reset isn't supposed to happen unless activated by the owner.
Please try > Clear Cache Files from the phone's System Partition Section > https://www.samsung.com/uk/support/mobile-devices/how-do-i-clear-the-cache-on-my-device/ You may need to insert your earphones or hook upto a powered On Laptop to access the Clear Partition Section. This may help with lag or stutters as this clears the phone of old/unused or broken cache files.There is also a Repair Apps option in the Menu System too.
If this happens again then if all your phone's software and apps are up to date and you don't use Apk files I'd suggest to let a Samsung Service Centre help.
If you use a theme or wallpaper that's been downloaded then consider removing them.
If I can be of any further help then please don't hesitate. Take care. 😎
Daily Driver > Samsung Galaxy s²⁵ Ultra 512Gb ~ Titanium Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help. " This is the way. "
