My phone suddenly swtiched off during gaming and it wiped all the data,randomly,Whats the reason?

so i was playing call of duty mobile with friends,then suddenly my phn switched off,then factory reset,except photos,photos remain,but saved contacts,apps,games,wallpaper,all other saved data,all gone,somehow photos remain....it happened so suddenly im still hsocked,whats the reason

Phone model: Oppo A92

Phone age:5-6 years almost