Null Reference Errors on Deconstruction of nested QML QtObjects

There is a null reference issue when QML QtObjects which were held by singletons get deconstructed. The structures contain theming information which is generated from data exported from Figma.

This issue appears sporadic, which is a strong indicator for a race condition. It appears at least on every fifth shutdown. In the attached example the structure of the theming classes is based on what is exported from Figma. Generator was used to manually build them on Linux (Ubuntu 20.04).

Steps to reproduce (only with Linux with the current example):
1) On Linux, build the attached example against Qt 6.3. or Qt 6.4.
2) Run the example
3) Close the example, it sometimes produces: "TypeError: Cannot read property <property_name> of null" warning before exiting normally.
4) If it did not produce the warning, redo the steps 2 and 3 until the warning is visible.