[Webkit-unassigned] [Bug 202696] WKWebView occasionally fails to render content when scrolling

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=202696

--- Comment #8 from teodor.atroshenko at gmail.com ---
More details. We can't reproduce this on iPad (with iPad OS). Earliest reports are from 12.4.1 (however 12.4 is possible). Reproducible all the way through iOS 13.2 Beta 1.

As mentioned in the previous comment, removing all evaluateJavaScript calls to WKWebView object stops the bug from being easily reproduced (we weren't able to reproduce it so far). Having at least one evaluateJavaScript call makes it appear but at a lower frequency than making all of the evaluateJavaScript calls that we normally make during loading.

Furthermore, when the bug occurs, JSContexts that are pending are not executed (when bug happens during loading, that means no JSContext is executed at all) until the freeze is resolved. The "unfreeze" happens either via an undetermined (likely random) timeout, sometimes by minimizing and restoring the app and everytime by mousing over the non-frozen WKWebView OR JSContext entry in Develop dropdown menu of Safari Preview.

To reproduce the bug again we no longer restart the app, we just issue location.reload() to the topmost WKWebView. The "success" rate of reproducing it is still about 20%. It can happen twice in a row or be okay for 10 consecutive attempts. We tried doing 5 times the regular evaluateJavaScript calls during loading (125 calls in total) and it doesn't seem to affect the rate of occurrence.

Please let me know what's the best way to capture the state of the app when it happens, so I can supply more relevant logs.

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