Found the problem...
Solution for me was, i removed all the certificates on OMV.
And was checking which PID was listening on my port 443 and 80 witrh the command lsof -i:443 , lsof -i:80. Strange enough my Plex was controlling port 443.
I stopped my Plex container. Rebuild Swag/Letencypt with port 443:443. Started first Swag and everything works. After that i started Plex. (maybe later i will check why Plex is using 443 (SSL) and/or if it's needed)
I'm happy 