aoo_client: couldn't establish connection with peer

I have this message when I join the same group on two different machines (OSX 10.15.4 and Windows10):

aoo_client: couldn't establish UDP connection to test|bar; timed out after 5 seconds

I tried under local network, and from external network using port fowarding, but still the same issue.
Also compiled aoo for raspberry Pi but got exact same problems.

Any Hints?

Cheers