crossplay not working anymore on Synology NAS (DS720+)

[Concretv]

Since yesterday, server does not seem to work anymore when "-crossplay" is specified in the SERVER_ARGS
Server is looping on :
PlayFab reconnect server 'ServerNAme'
Server 'ServerName' begin PlayFab create and join network for server
...

PlayFab login request worked (also got the "Register PlayFab server with IP..." message)
But after that it starts looping and server is unreachable

Everything works fine when "-crossplay" is removed

It reminds me an old issue that was fixed (and worked fine until yesterday)
Everything is up to date and, the strange part, everything worked fine and suddenly stopped working (without any modification/update to the docker image or the NAS since I was playing when it occured)

Is someone else having the same issue ?

UPDATE 1: setting SERVER_PUBLIC parameter to false has solved my issue !