Check the console (SHIFT + ~), most likely these are file conflicts.

The problem arises when some resource (sound, model, pictures, etc.) to which your mod refers (precache links, material->image, soundalias, etc) is not found in the files of your server, but nonetheless exists in other .iwd file in the client directory. Cvar "sv_pure" set to "0" (on server side) - solves the problem globally, but it is not advisable to use it if you want your mod to look the way you want it to