@bionade24 I just disabled seafdav in ngnix and the UI now works perfectly with wsgi 
Then I found Seafdav does not work (seafdav.pid problem) and in there is another link to Tutorial: Seafdav with WSGI behind Nginx. I followed the tuturial and now both ui and dav are running with wsgi.
Looks like the manual is outdated 
But I found following statement about seafdav from @DerDanilo
WSGI works just fine. CE manual contains the config.
Does somebody know where this CE manual is located? Looks like this manual is more current than this manual.