Pen input on laptop with extended display?

I use a 2in1 notebook that is compatible with a pen. When I transform my laptop into a tablet (display swiveled 360 degrees) I can write on it without problems. I have now connected a second monitor to my notebook as an extended display. Now my pen on my notebook is not working properly anymore. The touch works, but my pen does not write or write until I pick it up again and it does not work again. When I swing the display back and use it as a notebook, the pen input works again without any problems. Why is that and how can I fix the problem? Does anyone have experiences?

Have you looked in the manual, if the pen may only work (or general pens on this PC / notebook), when the display is turned?

I assume that it is "normal" that the pen input does not work when the monitor is connected.

Possibly. Let's contact the support of the notebook…