I am experiencing the same issue with my UEFN island, LORAN: ERUPTION.
The public island code, newly generated private versions, and even older private versions that previously worked are all stuck on “Finding Server”.
I tested from another computer using a different Epic Games account and the same issue occurs. I also tested another UEFN project, and that project successfully finds a server.
FortniteGame.log shows that the matchmaking ticket is successfully created but remains in TicketWaitingForAssigment without ever receiving a server assignment.
I also created my own bug report with additional logs and diagnostic information: UEFN island suddenly unable to create matchmaking servers – old private versions also affected - General / Issues and Bug Reporting - Epic Developer Community Forums
It appears that our islands may be affected by the same issue.