Here are the suggestions we would like to advise you:
Check if notifications are allowed in app info. (Tap and hold the app on home screen > app info > app notifications)
Please allow the apps to "auto start" in auto-start manager. (Mobile Manager > PowerMaster > Auto-start manager)
Check your battery optimization settings, and do not optimize the apps you wish to receive notifications instantly. (Settings > Battery > Battery optimization)
Check your battery mode, and choose Performance/Normal/Balance. (Mobile Manager > PowerMaster > Battery modes)
If the problem still appears, please tell me the app names and versions.
Thank you 🙂