My setup to descibe my problem:
I'm logged into a kde session at my desktop running plasmashell/plasma5 and kwin_x11.
As a user I start a TigerVNC that creates another x-display (with the "vncserver" command). The TigerVNC xstartup starts a xterm.
Now when i connect to the vnc server i get a black screen with a single xterm (as expected).
In the xterm i can type "kwin_x11 &" to get a windows boarders, but when i type "plasmashell &" it instantly quits doing nothing.
When i quit plasmashell on the actuall pc using "killall plasmashell" and then try again "plasmashell &" on the vnc session, plasma 5 starts as expected.

So my educated guess when i try to start plasmashell in the vnc session it detects the other plasmashell instance running on the physical x-server and quits itself.

Is it possible to have 2 seperate plasmashell instances running on the vnc x-display and the physical x-display?