Dynamic loading of a WPEView element fails due to the fact that the scene graph can be initialized already. In such case the sceneGraphInitialized signal is not received anymore and we need initzialize it ourself. There was a discussion on Github: https://github.com/Igalia/meta-webkit/discussions/236
Created attachment 426557 [details] Patch
Committed r276309 (236791@main): <https://commits.webkit.org/236791@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 426557 [details].