Qt3DWindow sometimes makes GUI disappear

[ashbob999]

We are using QT5.15.2 on Windows 10 and developing using C++ only (no qml).

We have an application which loads a model using a custom geometry renderer, and displays it to the scene using Qt3DWindow and QWidget::createWindowContainer, similar to the Qt 3D Simple Eample but all encapsulated into a class extending from QWidget.

The issue we are seeing is that on certain people's computers, the application is loading fine, but when the model loads the GUI widgets do not update graphically. if the app is minimised then maximised again the Qt3DWindow show correctly but the rest of the GUI turns black.
Image shows what it looks like (sensitive content removed).

The model is on one of many pages of a QStackedWidget, and the issue only happens once the page with the model on is shown.

However the GUI still reacts to user input, because I can click where the green box is and the QDialog still shows, and all QWidgets work perfectly.

This issue only seems to appear on certain computers, using Intel integrated graphics. Because if the app is forced to use a dedicated GPU (NVIDIA/AMD) instead, it works correctly.

Computers not working on:

• Intel i9, with integrated UHD graphics
• Intel i5, with integrated HD 530 graphics

What makes this issue stranger is that it works on a Win10 VM using Intel integrated graphics from the host (VirtualBox with 3D acceleration enabled).

It feels like an issue with opengl, where the Qt3DWindow takes priority and won't render the GUI.
We have tried setting Qt::AA_UseOpenGLES while this works for the main model, it breaks when we load other models in dialogs (failed to create context).

We would like to know the cause and if there is any fix.