P: Wrong size with Export As/Quick Export

I often use the quick export or the export as.. feature. Unfortunatly, the exported image has a different size (in pixels) than the original picture. Thats not only a different scale, but also a wrong canvas.
The results can vary even in one file when toggling different layers (randomly)

I have Windows 10 and the recent CC version installed.

Please let me know if you need more informations.