Please always activate the logs for error checking.
You activate this in the Nitrado web interface (the one with the dark background) in the general settings.
Then you can see the errors your server makes in the GIANTS web interface (the one with the light background) under Settings - Log files.
Should there be something with "Error: Could not start dedicated server with current mod setup because some dependencies are missing!"
Then a dependency is missing.
Missing dependencies means that there are mods in the moddesc.xml of the map that the map needs to run. If these mods are missing on the server, this message appears and the map or the server starts, but is not visible in the game list.
So either delete the dependencies from the moddesc and redistribute the map to all players (not recommended because buildings are usually missing from the map) or reload the missing mods.
Greets,
Steven