There are reports by some who have upgraded to iOS 9 that they see some apps crashing. This was first reported by CNET and from research, there are people in other online forums who are saying the same thing.
Here are some examples as seen on the CNET website;
“This iOS 9 update… App crashing and ugly fonts.” —@stephayson
“Y’all updated to iOS 9 for the extra hour of battery but you’ll regret it when it starts getting laggy and crashing” —@Nycphoria_186
“Outlook app is crashing after iOS 9 update. Had to uninstall and reinstall the app to get it to work again.” —@bananza
My personal experience
I upgraded to iOS 9 like many people and it was a good experience. However, I discovered that the new News app that comes with the upgrade was nowhere to be found at some point. I went to the app store and settings to see all installed apps and couldn’t find it. I even used the newly enhanced search bar to no avail. Then it occurred to me to restart my iPhone 5S. The app resurfaced though after the third restart. I wouldn’t say I have experienced cases of crash in particular and this could be the story across the world.
That said, iOS 9 is still worth the upgrade. It has a lot of enhanced features plus an improved font as well. You would have to upgrade to enjoy it.
When you experience a crash though, the first thing to check would be to see if there’s an update for that app. This is a newer version of an operating system and as such some apps may not work well with it. Other than that, if there’s an increasing report of crashing apps, Apple would have to issue a general fix which. That would be another upgrade to a more stable version of the app. Usually, initial releases of most software get these kinds of feedback.
Updating to a newer version of an OS is good especially if it’s coming from a reputable organisation.