I had the same issue with the Apple Watch. Pairing and unpairing seemed to do the trick. I also went to settings>notifications in the watch app on the iphone and turned off the notifications for apps, waited a few minutes, an turned back on the notifications. This last thing was recommended somewhere online.
PegasusTenma t1_j6iayuk wrote
Reply to Notifications aren't...notifying? by IcewolfTheBookish
I had the same issue with the Apple Watch. Pairing and unpairing seemed to do the trick. I also went to settings>notifications in the watch app on the iphone and turned off the notifications for apps, waited a few minutes, an turned back on the notifications. This last thing was recommended somewhere online.