QQuickWidget exploding in fragments on RPI

[davedelfino]

Hi QT-Community,
i ran into a problem which i don't know how to tackle.
Maybe someone can tell me, in which direction i have to look for or how the effect is namend, so i can better search the problem.

The program works fine for hours, then suddenly the image gets destroyed and is flickering all over the place in fragments:

https://www.veed.io/view/73dd6ff5-7601-4e80-81a3-81aee2985f13

Short description:
Crosscompiling QT5.15 for RPI using eglfs
Hardware: Raspberry Pi Zero 2 W

In a QQuickWidget is data displayed which is processed by a different thread.
The GUI updates when the thread sends a single "update"-signal to do so (~every 32ms).
All displayed Properties are connected to the same "update"-Signal.
While the thread is processing the data, the GUI is frozen via setUpdatesEnabled(false).

When i close the program after the faluire and try to start it again got the failure: "Illegal instruction".
After reboot everything works fine again for hours.

Many thanks for any help and happy christmas,
David