A week after iOS 9 was released officially, Apple is now rolling out a new update to address a couple of teething issues. It is available now as an OTA (Over The Air) update and you can check manually under Settings > General > Software Updates.
The changelog reads as follows:
Fixes an issue where some users could not complete setup assistant after updating
Fixes an issue where sometimes alarms and timers could fail to play
Fixes an issue in Safari and Photos where pausing video could cause the paused frame to appear distorted
Fixes an issue where some users with a custom APN setup via a profile would lose mobile data.
This is also applicable for the iPad and iPod Touch that supports iOS 9. The iOS 9.0.1 update is about 30MB and it shouldn’t take too long to download compared to the massive 1GB file for the initial iOS 9 release.