I noticed this when my son told me that I had missed some important information this week from the primary school he attends, and that he had been told that I should have seen an alert from the Skoolbag app (a fantastic app that his school uses to notify parents of school-related matters - reminders, newsletters, notices).
So I checked my settings in Settings -> Notifications for this app and they were all correct - showing that I should have been getting Alert notifications all along.
My clever 11yo son turned off the Allow Notifications setting for the Skoolbag app, and then turned it back on. This immediately caused the latest alert to pop up.
So it might be worth checking if you are perhaps missing important notifications from any of your Apps since you upgraded. I'll certainly be checking all mine by turning the Allow Notifications off then back on for the important ones.