devtrackers.gg
Are you playing solo? If so I think there’s a daily XP cap.
And if you're playing online, it could he a variety of reasons such as a restricted xp experience in Battlefield Portal.
But if its within All Out Warfare I'd give the game a reload! Please don't be alarmed either, it may read as zero but it is all saved information within our servers, so you should still be levelling on up.