[Webkit-unassigned] [Bug 257965] New: Safari occasionally locks up and stops completing XHR requests

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=257965

            Bug ID: 257965
           Summary: Safari occasionally locks up and stops completing XHR
                    requests
           Product: WebKit
           Version: Safari 16
          Hardware: iPhone / iPad
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebKit2
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: webkit-bugzilla at cuzzo.net
                CC: kkinnunen at apple.com

I am a developer at a company that hosts a web application that is heavily used by iOS users. Starting a couple months ago, we saw a decrease in conversion metrics.

After investigating, we discovered strange behavior happening to iOS users, starting with iOS 16.4 (also seen on iOS 16.5). At some point in the session, a API request would appear to hang, eventually timing out (the application times out the request, this timeout is not from iOS or Safari itself). >From that point on, all XHR requests fail to resolve and are eventually timed out as well. This behavior is observed via a front end event recording service (FullStory). After this happens, the tab seems to be "fouled" and all requests fail.

We are confident network conditions are fine in a majority of these cases are these are not "true" timeouts. We have been able to replicate the issue on personal iOS devices, but not reliably. 

We believe this issue could be related to Bug 255524 due to new cookies often being set around the time the bug appears and the fact that we were not able to replicate the bug in a private window. However, we decided to make a new bug report as the impact we're seeing is different than what is reported in that thread.

Personally reproduced with:
 - iPhone 13 Pro running iOS 16.5

Additional info:
 - This bug could also be present on MacOS Safari as we've seen a couple sessions that appear to show this behavior on those devices. We however see much more traffic from mobile iOS so we see it there most often.
 - The first call to hang/timeout is not always the same call, or even in the same user flow in the application. We also haven't seen this behavior on any other browser. Given this, we're confident the issue isn't with the application itself and is most likely a Safari bug.
 - I have seen this behavior from a user perspective while interacting with other sites day to day on my iPhone. A tab will lock up and be 'loading' the site indefinitely. The only thing that resolves the issue in this case is closing the tab and opening a new one.

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