Friend of mine just had this happen. His issue was an email that was stuck (believe pictures in the email), anyway a restart forced the email to finally come through.
I have had it happen to me several times. I know the causes for mine though. I share my Apple ID with my mom, brother & wife so that we never have to repurchase an app/song/movie etc.
Anytime I notice the spinning wheel I check the follwoing:
- Apps try to download (may have started on wifi) and moving to cellular causes them to pause or move slowly.
- Music. Either songs or albums downloading.
- Updates not completely getting downloaded. (may need to check App Store in settings to see if set to use cellular for auto downloads)
I'm pretty sure mine is always one of those scenarios. So not sure if you share yours or not, but hopefully that helps or points you in the right direction to check some options.