My Samsung S8's notifications won't show up.

[Android Central Question]

Some notifications show up and some don't. When I'm on my phone, notifications work perfectly fine but when my phone turns off notifications don't show up. Youtube and all the apps that are already on the phone when you first start it, like gmail and messages, work perfectly fine, but, apps that I download sometimes don't send notifications. Youtube works but some others don't or sometimes show up as a weird pattern. For example, a game called "Mystic Messenger" has chat rooms and I noticed that there is a pattern. After missing 2 chat rooms (since my phone doesn't show the notification for a new chat room opening) I finally get a notification for a new chat room. So, it looks like this,

[missed chat room] [missed chat room] [didn't miss chat room] [missed chat room] [missed chat room] [didn't miss chat room] [missed chat room] [missed chat room] [didn't miss chat room]

I'm pretty sure the app is o.k because when I had an iPhone, the phone always sent notifications to me. Mystic Messenger was one example, there are other apps that have similar or the same problem.

Before you ask, I already checked,
[Settings => Notifications => turn on "Allow notifications"] I even turned on "Set
as priority" for the apps with notification problems.

 

[B. Diddy]

Welcome to Android Central! Any power-saving modes turned on? Look for a Battery Optimization option in the system settings, and see if it helps to turn off optimization for one of those apps.

Also, is Restrict Background Data/Data Saver turned on?