The following two API tests are consistently asserting on iOS simulator debug bots after https://commits.webkit.org/256048@main landed: TestWebKitAPI.CopyHTML.SanitizationPreservesCharacterSet TestWebKitAPI.CopyHTML.SanitizationPreservesCharacterSetInSelectedText ASSERTION FAILED: m_clients.contains(&client) platform/graphics/FontCache.cpp(400) : void WebCore::FontCache::removeClient(WebCore::FontSelector &) 1 0x11c7423d9 WTFCrash 2 0x173fc22eb WTFCrashWithInfo(int, char const*, char const*, int) 3 0x178ec7f36 WebCore::FontCache::removeClient(WebCore::FontSelector&) 4 0x177529c61 WebCore::CSSFontSelector::~CSSFontSelector() 5 0x177529f25 WebCore::CSSFontSelector::~CSSFontSelector() 6 0x177529f89 WebCore::CSSFontSelector::~CSSFontSelector() 7 0x17707d4bc std::__1::default_delete<WebCore::FontSelector>::operator()(WebCore::FontSelector*) const 8 0x17707d487 WTF::RefCounted<WebCore::FontSelector, std::__1::default_delete<WebCore::FontSelector> >::deref() const 9 0x17752dd59 WebCore::CSSFontSelector::deref() 10 0x177534c49 WTF::Ref<WebCore::CSSFontSelector, WTF::RawPtrTraits<WebCore::CSSFontSelector> >::~Ref() 11 0x177529325 WTF::Ref<WebCore::CSSFontSelector, WTF::RawPtrTraits<WebCore::CSSFontSelector> >::~Ref() 12 0x177a1bdc9 WebCore::Document::~Document() 13 0x177f8342f WebCore::HTMLDocument::~HTMLDocument() 14 0x177f83455 WebCore::HTMLDocument::~HTMLDocument() 15 0x177f83539 WebCore::HTMLDocument::~HTMLDocument() 16 0x177a1e673 WebCore::Document::decrementReferencingNodeCount() 17 0x177a1df47 WebCore::Document::removedLastRef() 18 0x177c0b034 WebCore::Node::removedLastRef() 19 0x17412c8dc WebCore::Node::deref() const 20 0x174fe3a7e WTF::DefaultRefDerefTraits<WebCore::Document>::derefIfNotNull(WebCore::Document*) 21 0x174fe3a49 WTF::RefPtr<WebCore::Document, WTF::RawPtrTraits<WebCore::Document>, WTF::DefaultRefDerefTraits<WebCore::Document> >::~RefPtr() 22 0x174fe37c5 WTF::RefPtr<WebCore::Document, WTF::RawPtrTraits<WebCore::Document>, WTF::DefaultRefDerefTraits<WebCore::Document> >::~RefPtr() 23 0x178726157 WebCore::DocumentWriter::begin(WTF::URL const&, bool, WebCore::Document*, WebCore::ProcessQualified<WTF::UUID>, WebCore::NavigationAction const*) 24 0x17871d96d WebCore::DocumentLoader::commitData(WebCore::SharedBuffer const&) 25 0x1262426d3 -[WebFrame(WebInternal) _commitData:] 26 0x12631ddc6 -[WebHTMLRepresentation receivedData:withDataSource:] 27 0x12622c15a -[WebDataSource(WebInternal) _receivedData:] 28 0x12622301c WebFrameLoaderClient::committedLoad(WebCore::DocumentLoader*, WebCore::SharedBuffer const&) 29 0x17872526e WebCore::DocumentLoader::commitLoad(WebCore::SharedBuffer const&) 30 0x178726e13 WebCore::DocumentLoader::dataReceived(WebCore::SharedBuffer const&) 31 0x17875ff90 auto WebCore::DocumentLoader::continueAfterContentPolicy(WebCore::PolicyAction)::$_9::operator()<WTF::Ref<WebCore::SharedBuffer, WTF::RawPtrTraits<WebCore::SharedBuffer> > >(WTF::Ref<WebCore::SharedBuffer, WTF::RawPtrTraits<WebCore::SharedBuffer> >&&) const Child process terminated with signal 11: Segmentation fault https://results.webkit.org/?suite=api-tests&suite=api-tests&test=TestWebKitAPI.CopyHTML.SanitizationPreservesCharacterSetInSelectedText&test=TestWebKitAPI.CopyHTML.SanitizationPreservesCharacterSet