Yeah, there are a lot of synchronous network calls in many applications. I ran out mobile bandwidth recently and have spent the last week in AT&T's penalty box and it's amazing what broke. For example, Audible's app goes to complete hell in this state when you launch it; you can bypass the hang by clicking library but it would be content to mostly just sit there.
I found a fun issue with the Apple Music app- if you're connected to wifi but NOT connected to the internet, it takes 60 seconds for the app to respond when you try to play something or change tracks.