We have observed an issue where upgrading an iPhone to iOS 18.4 causes installed apps to revert to significantly older versions. For example, if the App Store version is 1.0.284 and the user had 1.0.283 installed before the upgrade, after updating to iOS 18.4, the app version reverts to 1.0.208—which is nearly a year old.
We suspect this may be related to iCloud backup restoration. Has Apple encountered similar cases, and is there a known resolution for this issue?
If iCloud backup is not the cause, another possibility is that when the user downloads the app from the App Store, they are actually receiving a binary diff patch. The system update may have removed these previously installed patches, causing the app to revert to its original base version.
This issue started occurring on April 1st at 5:00 PM UTC.
Calculation error, the correct time is March 31st at 5:00 PM UTC.