I have to come back to a previous issue (Resilio Sync not listening to port 3838 on Ubuntu 20.04) which hasn't been solved.
In many case LAN search is not working for the Resilio Sync client on my Ubuntu 20.04 server as Resilio Sync is not listening to multicast on port 3838, which is required to LAN search. This happens often after a reboot and if a do a service restart of the resilio sync process it is always the case.
If everything is fine netstat -npl |grep rslsync showstcp 0 0 192.168.1.2:40935 0.0.0.0:* LISTEN 2448/rslsynctcp6 0