Summary
I'm using Background Assets to download Apple-hosted Asset Packs(downloadPolicy = onDemand). The first
download cancellation succeeds, but on the second and subsequent downloads,
progress.cancel() fails to work and the download completes to the end.
Environment
- iOS 26.0 – 26.3 RC (all produce the same result)
- Xcode Version 26.2 (17C52)
- Using Apple-hosted Asset Packs
Steps to Reproduce
- Start downloading an Asset Pack
- Call progress.cancel() during download → Succeeds
- Start downloading the same Asset Pack again
- Call progress.cancel() during download → Fails (download completes to the end)
Observed Error Logs
After 1st cancellation: A download with the ID "X-XXXXXXXX-XXX" failed: Error Domain=NSURLErrorDomain Code=-999 "cancelled"
↑ This is expected (cancellation succeeded)
The fact that version 0 of the asset pack with the ID "X-XXXXXX-XXX" finished being downloaded couldn't be reported: Error Domain=NSCocoaErrorDomain Code=3851 "Property list invalid for format: 200 (property lists cannot contain objects of type 'CFError')"
↑ Problem: Unable to serialize CFError to plist
2nd cancellation attempt: The download with the ID "X-XXXXXX-XXX" couldn't be canceled: Error Domain=BAErrorDomain Code=113 "The requested download operation failed because the download object did not exist."
↑ The download object we're trying to cancel supposedly doesn't exist
Implementation Code
// Cancel implementation func cancel(tag: String) async { let statusUpdates = AssetPackManager.shared.statusUpdates(forAssetPackWithID: tag) for await statusUpdate in statusUpdates { if case .downloading(_, let progress) = statusUpdate, progress.isCancellable { progress.cancel() } } }
Analysis
It appears that when the first cancellation occurs, the system internally tries to save the cancellation state to a plist, but fails to serialize the CFError object. This seems to cause an inconsistent internal state, preventing the system from correctly recognizing the download object on subsequent downloads.
Questions
- Is there a workaround?
- Is there a planned fix for a future iOS version?
Hello! That definitely looks like a problem! I think that you’re encountering two separate issues: one with download cancellation and another with internal analytics.
For the former issue, we’ll try to reproduce it on our side. It would be super helpful if you could file a feedback report in Feedback Assistant, making sure to attach sysdiagnose logs from the device on which asset-pack cancellation failed soon after reproducing the behavior. Plus, filing a feedback report ensures that you’ll be automatically notified when we fix the issue. We’ll let you know if we figure out a workaround before the fix is available. Thanks!
The fact that version 0 of the asset pack with the ID "X-XXXXXX-XXX" finished being downloaded couldn't be reported: Error Domain=NSCocoaErrorDomain Code=3851 "Property list invalid for format: 200 (property lists cannot contain objects of type 'CFError')"
That error message concerns the latter issue. If you installed the app from TestFlight, then the system collects data about successful, failed, and canceled downloads to help with identifying issues during testing. If you installed the app from somewhere else, such as Xcode or the App Store, then those data are never actually sent anywhere. Either way, regardless of whether the analytics would’ve actually been sent, an error there should have no functional impact on your app or its asset packs.