This is a version issue with the updated game and the version Nitrado has on atm.
Nitrado servers are on version 346.30.
the latest update brought the players version to 347.1.
Because of this mismatch, the server is not visible untill nitrado rolls out the game update to the servers. (In the interface they put out a message that they are working on it)
"We are aware of a missing update on your ARK server. We are already in the process of deploying it and should arrive to your server soon."
*Edit, the mismatch only happenes when a version changes (example, 346 to 347 in this case). if its minor, the number behind the decimal changes and there is no issue