Can you post the command line you use to start the server? e.g. mine is -console +maxplayers 24 -game garrysmod +host_workshop_collection 143148073 -authkey <myauthkey> +gamemode cinema +map Cinema_Theatron

Make sure you have all of the content for the map. cinema_theatron requires more than just the bsp file.

The command line I use is srcds.exe -console -game garrysmod +map cinema_theatron +gamemode cinema +maxplayers 16 +host_workshop_collection 129751070 -authkey (key).
And I have the cinema gamemode and the theatron map from the workshop in that collection, is there anything else I need to do to make it work?

Try placing 'gamemode cinema' in cfg/autoexec.cfg

Since you're trying to run Cinema, I think the addon collection you are using has a /lot/ of unnecessary addons. Nothing more than what is in the collection Sam made should be needed. It is possible that one of those addons is conflicting with Cinema, hence your problems. To test this theory, try making a fresh server install using the collection 143148073 instead of the one you are currently using. If it works, you can assume it was something in your collection that was causing the problems.

Running it on a fresh server solved the problems, thank you. The only addon I'll be running on it apart from the cinema addons is evolve, and that seems to be causing no problems