UBook Pro not charging while adapter is plugged in USB-C

Hi all!

I have an USB-C adapter to connect my standard HDMI screen to my UBook Pro. However, when I plug this adapter into the USB-C port of UBook, it stops charging with the original charger, and battery discharges after a few hours, even if charger is plugged.

It seems like, if there is something plugged in the USB-C port, Ubook assumes it will be charging through USB-C and stops charging through the normal port.

Any clue why this could be hapenning and how to fix it?

Thanks in advance!