BGContinuedProcessingTask code pauses when device is locked

The documentation does say "The system can terminate a continuous background task abruptly depending on run-time conditions"

Of course both the documentation and the API are in pre-release state and the final state could be different than what you are expecting.

In any case, this is something our engineering teams should investigate.

We'd greatly appreciate it if you could open a bug report, include crash logs and sample code or models that reproduce the issue, and post the FB number here once you do.

Bug Reporting: How and Why? has tips on creating a successful bug report.

I haven't seen anything in the documentation regarding execution of tasks while the phone is locked. So I'm a bit confused if I encountered an iOS bug here?

It's possible there's a bug on our side as well, but the issue in your code is that you never call setTaskCompleted(success:) to finish the task. As far as the system is concerned, your task isn't "done" until you mark it complete, regardless of progress. That means it eventually fails due to lack of progress once your loop stops and the block returns.

Is it finishing properly while the device is unlocked? That's actually what's odd here to me.

__
Kevin Elliott
DTS Engineer, CoreOS/Hardware

Sorry for the late response. Just got around to testing it on iOS 26 beta 8.

It's still the same as before, but when locked it doesn't always fail the task. But it remains paused and doesn't progress until I wake up the screen.

Feedback ID: FB19916760

I've also added setTaskCompleted(success:) and now it shows a tick when the background task is complete.

It's still the same as before, but when locked it doesn't always fail the task. But it remains paused and doesn't progress until I wake up the screen.

Feedback ID: FB19916760

Thank you for that and this is definitely a bug. The API was intended to keep the device awake, but an oversight meant that if left off the assertion exception that prevented sleep, creating the odd behavior you're seeing. Note that the behavior here isn't directly tied to the device locking, so any other activity that keeps the locked device awake will also mean the task continues to run.

I suspect this is also why I haven't seen more reports of issues with this as LOTS of things prevent idle sleep, but in terms of development usage patterns and real-world device usage.

In any case, we'll either fix the assertion to keep the device awake (this is what I expect), or we're going to need to update the documentation to try and describe what's going on.

__
Kevin Elliott
DTS Engineer, CoreOS/Hardware

I'm glad I found this thread because we're experiencing exactly the same thing. We're uploading a large-ish (hundreds of MB) file to AWS S3 and using a BGContinuedProcessingTask to show the progress. The actual upload happens in the background using the AWS S3 SDK. Everything goes fine until we lock the screen, then the BGContinuedProcessingTask is expired even though the upload is still ongoing.

Is there any resolution on the horizon for this issue? Would it help if I file a Feedback Assistant report or can I join an existing one?

Is there any resolution on the horizon for this issue?

Have you specifically tested this in iOS 26.1? FB19916760 should have been fixed in that release.

Would it help if I file a Feedback Assistant report or can I join an existing one?

If it's happening on 26.1, then the next step is to test in the latest seed* of iOS (iOS 26.2 beta 3/23C5044b). If it's still happening there, then please file a bug, upload sysdiagnose, and then post the bug number back here.

*This both makes sure it's still happening and avoids being asked to reproduce on the latest seed.

__
Kevin Elliott
DTS Engineer, CoreOS/Hardware

Hi Kevin,

I just did a quick test on 26.1 and the issue still happens: the BGContinuedProcessingTask is expired even though the upload is progressing and actually completes. I'll have to do more testing to confirm, but it appears to me that this only happens with the screen truly locked (lock icon showing in the status bar/dynamic island). When Face ID has seen me and the lock icon disappears, the BGContinuedProcessingTask is updated properly.

We're going to give it a try on iOS 26.2 beta as well and if it still happens, I'll make a FB report.

It is also failing on iOS 26.2 Beta 3. I've filed a Feedback Assistant issue: FB21233240

I tried again, starting an upload then backgrounding the app by hitting the side button, keeping the lock screen unlocked (no lock icon). Again the BGContinuedProcessingTask kept updating progress, after which it (correctly) reported the upload as completed. So I think it is safe to say that the issue only happens when the device is truly locked.