QComboBox popup animation weirdly offset to the left

After upgrading my apps to Qt 5.12.1, there seems to be an issue with the animation of all QComboBox popups. After clicking on the combo box, the initial position of the popup is around 10 pixel to the left of the combo box itself. Only when the animation is complete and the complete popup is shown, is the position adjusted again.

There is also a StackOverflow issue referencing the same problem from PySide2:

https://stackoverflow.com/questions/54445028/qcombobox-popup-animation-glitch