Notifications don’t appear when watching videos

I have been getting this issue ever since I started using the Galaxy J4 Core phone. I moved from the S Series to the J series and now whenever I’m watching videos on YouTube I don’t get notifications from other apps until I later click on those apps to see the many messages I got. One instance is that I don’t get messages from Facebook Messenger when I’m using YouTube. I have even adjusted the settings under “Apps that Appear on Top” but still no luck. What could be the issue here ? Please help.