I was having the same discovery network unreachable error but the solutions here did not work for me.
I’m running Home Assistant Docker on unRAID server.
As it turns out, something else is using the same port that netdisco was trying to use.
Found that by running python3 -m netdisco inside my container which spit out OSError: [Errno 98] Address in use
Changed the port netdisco was using by editing /usr/local/lib/python3.7/site-packages/netdisco/daikin.py line 10 UDP_SRC_PORT = 30000 to use 30005 instead.
Temporary solution as it won’t survive upgrades, but a quick fix. Looks like netdisco is depreciated anyway and will probably eventually be removed, so I’m stopping there…
python3 -m netdisco dump now shows my devices properly.