My PC:
Windows 11 Home
NVIDIA GeForce RTX 3050 Ti Laptop GPU

I made screenshots with description.  (I animated my character and one of the animated controls causes a bug with a long forehead stretch.) In restpose everthing is fine. I tested and found out, it must be specific animated controls with trigger the issue. )

Thank you for the report, you are importing it as gltf/glb ? If you are reimporting the model in blender (like the exported one) it still looks fine ?

I import it as a .blend into pixelover.

I´m not sure I understand your second question.  Can you clarify it for me?

(In blender the model looks completly normal. I have control curve objects to animate the model.)

Yes, this will be improved in the future. For now, when importing a Blender model into PixelOver, the process involves converting it to a GLB file first (it does in the background so it's transparent for users). But you can try exporting your model as GLB from Blender, then reimporting it back into Blender to check if anything breaks during the conversion.

Alright thank you Deakor :)

(I tried the .glb conversion, but no difference :I)