App hangs v2 report very high (and invalid) durations

[ghugues]

Platform

iOS

Environment

Production

Installed

Manually

Version

8.54.0

Xcode Version

26.0

Did it work on previous versions?

Yes, before we enabled app hang tracking v2

Steps to Reproduce

Enable App Hang tracking v2.

Expected Result

App hangs report the actual hanging duration, if any.

Actual Result

Sentry reports very high hanging duration when breadcrumbs clearly show the app was not hanging.

Example: https://amoamoamo.sentry.io/issues/6769842273/events/26d3dc95c61642e38eb2bb737bcbbac2

In this example, not only the main thread is not blocked (according to the stack trace), but breadcrumbs show that "App lifecycle foreground" ran just before hang detection. Since this event can only be fired from the main thread, the main thread was not blocked.

This report is a reopen of #5907

Are you willing to submit a PR?

No response

[linear]

COCOA-764

[philipphofmann]

Thanks for reporting this @ghugues. Can you by any chance reliably reproduce this?

We also have a customer who most likely has the same problem; see Notion.

[philipphofmann]

We also observe this phenomenon in one of our sample apps. We should be able to find the root cause.

[philipphofmann]

I identified a problem that occurs when apps move from the background to the foreground, which causes us to falsely report app hangs. It's likely that this solves some or all of these app hangs. I'm going to open a PR soon.

[ghugues]

@philipphofmann I haven't tried to reproduce it no. But we have thousands of reports like the one I linked in production.