Subbrn first be aware of this
Custom maps are not written with hot-joining in mind, because ZM dedicated servers didn't exist before Plutonium
This means most of the custom maps code are not written with this in mind and therefore they will have bugs on dedicated servers that cannot be fixed without rewriting their code
Now, the issue might be that you didn't update your CFG (map rotation) accordingly.
The map name has to be the result of the mapname dvar in the console, which can also be the correct .ff file's name in the map's folder