identifierForVendor changes on reinstall
identifierForVendor is not supposed to change on reinstall of app:
The value in this property remains the same while the app (or another app from the same vendor) is installed on the iOS device. The value changes when the user deletes all of that vendor’s apps from the device and subsequently reinstalls one or more of them. The value can also change when installing test builds using Xcode or when installing an app on a device using ad-hoc distribution. Therefore, if your app stores the value of this property anywhere, you should gracefully handle situations where the identifier changes.
https://developer.apple.com/reference/uikit/uidevice/1620059-identifierforvendor
However, I've just tested this with one of our live apps on the app store. Even with a number of other of our apps still installed on the device, if I reinstall app A the UUID returned from identifierForVendor changes every time.
It was not like this.
This used to work. But at some point, the UUID seems to have started changing on "simple reinstalls" (as stated above). Is this a known bug? Is identifierForVendor known to be broken versus the documentation above? Any workarounds (other than saving UUID to keychain, because that method breaks with iCloud syncing)?
Answer
It's a known bug. It seems like Apple made an update to AppStore that causes this new behavior for identifierForVendor around the 28:th May. If you search in the App Developer forum, there are other developers reporting the same problem.
The signature gc from Apple have replied on the issue with the following answer: "Please file bug reports on this at https://developer.apple.com/bug-reporting>. We're aware of this issue and are investigating. There's no known workaround at this time."