Bug 298222 – REGRESSION (iOS 18.6): Page load takes ~24s in Safari/WebView

• Status: RESOLVED
• Resolution: DUPLICATE
• Component: CSS

[Neetu]

Product: WebKit (Safari / iOS)
Version: iOS 18.6 (WebKit 618.x – exact version if possible)
Hardware: iPhone 14 / iOS 18.6 (also reproducible on other iPhones)

Steps to Reproduce

Open Safari on iOS 18.6 (or any WKWebView in an app).

Navigate to [dentsplysirona.com/de-de]

Observe load time and rendering.

Expected Results

Page loads in ~2–3 seconds (normal load time on iOS 18.5 and earlier).

Layout renders progressively, no long blocking tasks.


Actual Results

Page takes ~24 seconds to fully load.

Rendering stalls before first paint.

Same page on iOS 18.5 loads quickly, so this appears to be a regression introduced in 18.6.

Additional Notes- 

Issue affects both Safari and in-app WebViews (WKWebView).

Desktop Safari 18 (macOS) does not show this issue.

Clearing cache/cookies does not help.

Happens consistently across multiple sites with moderate JavaScript and CSS payloads.

Possibly related to JS parsing/render pipeline regression introduced in iOS 18.6.

[Neetu]

Hi [e-mail] are there any updates?

[Alexey Proskuryakov]

*** Bug 298226 has been marked as a duplicate of this bug. ***

[Alexey Proskuryakov]

I can reproduce that the page loads quickly in iOS 18.4.1 (don't have 18.5 handy). Both iOS 26 and macOS 26 show the same issue which is similar to one reported, except that the page does get some content painted before stalling.

[Radar WebKit Bug Importer]

<rdar://problem/159670991>

[Ganesh Muddliyar]

Do we know by when this will be fixed?

[Simon Fraser (smfr)]

The page is spending a lot of time in CSS selector code:

      2405 ???  (in <unknown binary>)  [0x10f644044]
        2405 WebCore::jsDOMTokenListPrototypeFunction_add(JSC::JSGlobalObject*, JSC::CallFrame*)  (in WebCore) + 228  [0x1b54577c4]
          2405 WebCore::DOMTokenList::addInternal(std::span<WTF::AtomString const, 18446744073709551615ul>)  (in WebCore) + 332  [0x1b6b2bd28]
            2405 WebCore::DOMTokenList::updateAssociatedAttributeFromTokens()  (in WebCore) + 612  [0x1b6b2c6c0]
              2405 WebCore::Element::setAttribute(WebCore::QualifiedName const&, WTF::AtomString const&, bool)  (in WebCore) + 264  [0x1b68f2fb8]
                2405 WebCore::Element::setAttributeInternal(unsigned int, WebCore::QualifiedName const&, WTF::AtomString const&, WebCore::Element::InSynchronizationOfLazyAttribute)  (in WebCore) + 564  [0x1b68fda04]
                  1338 WebCore::Style::AttributeChangeInvalidation::invalidateStyle(WebCore::QualifiedName const&, WTF::AtomString const&, WTF::AtomString const&)  (in WebCore) + 3656  [0x1b7984128]
                  ! 1127 WebCore::CSSSelectorList::makeJoining(WebCore::CSSSelectorList const&, WebCore::CSSSelectorList const&)  (in WebCore) + 200  [0x1b66454c0]
                  ! : 714 WebCore::CSSSelector::CSSSelector(WebCore::CSSSelector const&)  (in WebCore) + 212,216,...  [0x1b4ca3290,0x1b4ca3294,...]
                  ! : 413 WebCore::CSSSelector::CSSSelector(WebCore::CSSSelector const&)  (in WebCore) + 232  [0x1b4ca32a4]
                  ! :   321 WTF::fastMalloc(unsigned long)  (in JavaScriptCore) + 396,12,...  [0x1b098049c,0x1b098031c,...]
                  ! :   49 bmalloc_allocate_casual  (in JavaScriptCore) + 72  [0x1b221fe94]

[Simon Fraser (smfr)]

This was fixed in 299018@main.

*** This bug has been marked as a duplicate of bug 297591 ***