I got an infinite loop when using QWebEngineView, this way:

• I create a QWebEngineView, and call setHtml()
• During the Html loading, the "RenderWidgetHostViewQtDelegateWidget::setKeyboardFocus" calls "QGuiApplication::sync()"
• If the page takes more than 5 seconds to load, my application aborts and tries to load another QWebEngineView, posting a message to Qt
• This new QWebEngineView receives the message to load during this QGuiApplication::sync, and starts the same loop all over again.

This really isn't a "normal" application flow, but the point is, I thing calling QGuiApplication::sync is a very bad idea, many things can happen in the event loop, even deleting the currently running QWebEngineView.

The QGuiApplication::sync comments even says:
"This function is timeconsuming and its use is discouraged."

This was the commit that introduced this:

http://code.qt.io/cgit/qt/qtwebengine.git/commit/src/webenginewidgets/render_widget_host_view_qt_delegate_widget.cpp?id=01c029fd90162bdbbcf9534537f26138a333c570