Socket error unless I connect and disconnect with AnyDesk

[trevix]

This is a bizzarre one:

My standalone connects as a client to an Android 11 standalone that acts as a server (I am using port 54321 on local network), using sockets on WiFi.
Connection works fine on all devices.

The other day I was in a place where they had WiFi access points and, not matter what, I could not establish a connection.
Note the following:

• Ip of the server is correct (local)

• No firewall is open

• The IP is set as static on the server device and reserved on the router

• On the client device wifi setting, the address is NOT set to private (to avoid change of MAC if moving from AP to AP)

• Tests have been done anyway always in the same physical position (this way there should not been a connection change to a different AC)

After serveral unsuccessful tests, I connected with "AnyDesk" to the server device, then disconnected AnyDesk:
from then on, my socket connection worked as expected, until the next restart of the server device.

What can explain this behaviour? It is like if the temporary AnyDesk connection opens a door and leave it open...
Thanks for any help or suggestions
Trevix