x11nvc display is vertically displaced

I want to connect via VNC to my workstation. I have access to the box via SSH over a VPN. On my workstation I start my VNC server like this x11vnc -rfbport 5901 -rfbauth /home//.vnc/passwd -usepw -display :0 OS is a Cenots7. I'm only user and have no sudo or root privileges. My VNC client can connect to the server and I confirmed that keyboard and mouse events arrive at the server with -dp and -dk. However, the image I get of my workstation desktop is shifted down vertically by a few hundred pixel thus creating a black box at the top and the bottom is cut off. Additionally the workstation does not react to any input. I made sure the workstation has a monitor connected that is switched on. I'm searching for hours but can't find a clue on what's going on. Maybe I find help here.