TechRepublic.com has a good article on troubleshooting 8 known issues with iOS 8. The issues they cover are
- Wi-Fi connectivity issues
- Battery drain
- Safari slow page loads
- Low volume through earpiece during phone calls
- iMessage errors/can’t connect to server
- Apps not updating/stuck downloading
- Slowdowns/sluggish behavior
- No phone calls in or out
If you are having any of those issues, you can check out their possible solutions.