There have been a lot of reports of iOS devices crashing and encountering different issues in iOS 9 and Apple was quick to release a fix for those.
iOS 9.0.1 fixes the following issues:
– Fixes an issue where some users could no 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 cellular data.
iOS 9 currently has the highest adoption rate, with more than 50% of the devices now updated to iOS 9 only after a week of its release.