It ist not a firewall a Firewall, open Port or Antivirus topic. All Resilio Sync clients are in the lokal LAN and it works wit the Windows clients.
Rslsync ist just not binding to the necessary ports when it starts. When I trigger a network reconfiguration I does so and it works until rslsync is restarted again. Seems an issue of the Linux version of rslsync.