Hello dmystp,
To start, you'd want to provide more specific details on what type of notifications you're talking about. Do you mean notifications in the Notification Center? Are you talking about badges (red dots on the app icon)? Are you talking about sounds/vibrations?
Depending on the type of notification you're trying to receive, you'll want to make sure you have that notification type enabled for the application.
Use notifications on your iPhone or iPad
In Settings > Notifications > Scheduled Summary, you'll also want to make sure you don't have the notifications scheduled to only come in at a certain time.
Aside from that, you'll want to check Settings > Focus to make sure you currently don't have Do Not Disturb or a Focus turned on.
Use Focus on your iPhone or iPad
If everything is set up properly for the notifications you're trying to receive and they're still not coming in, then you'd want to contact Apple to report that issue: Get Support
Cheers!