WD19 worked with Thinkpad P1 Gen 2, no monitor signal with Thinkpad P1 Gen 3

I had my WD19 thunderbolt docking station working just fine with my Thinkpad P1 Gen 2. Charching, USB keyboard, external monitor via DisplayPort just worked fine after plugging everything together.

My notebook just got upgraded to a Thinkpad P1 Gen 3, I plugged it in and everything continued working, EXCEPT the external monitor via DisplayPort.

The problem stays the same on Windows 10 and Ubuntu 20.04. Via Windows I updated the WD19 firmware successfully, but nothing changed.

I already checked the monitor, it works fine as an external monitor via HDMI directly connected to the notebook, Connecting the same cable via HDMI to the docking station led to the same results: no signal to the monitor.

What is my next troubleshooting possibilty? Thanks in advance!