Using Attached example, if two window (Menu->Open Web Ui->inMainwindow and in AnotherWindow ) are open it takes a while to render window in MDI. Further if open Summary Ui is opened then it makes it worse, even dragging/moving mdi window lags.

This whole thing become even more slow if application is being run on another machine and VNC is used.

The most significant inconvenience is that the slow down persists even after destroying the QWebEngineView object.