Go to security - permission auto run management and give permission to the apps you want… The same to notification management the same in app management…
Then go to security - power - app management and do the same but there is very important to give permission also in google services and google framework…
Then the last thing to do is open recent apps and lock the apps you want by tapping and holding your finger on them… You will see a small locker in the app.
If you do all these you won’t have any problem with notifications again.
@jiricekk that’s not what I told you to do!
Okay wait… you did it all.
Did notifications every work for you? Do you have a stable Internet connection on your phone?
Was your phone rooted previously? And if so, did you update + clear data?