I found a problem with the packaging: ctf_longplace_v12.pk3 breaks textures and shaders on some other maps.
You are allowed to include modified textures and shaders from the official Xonotic releases, but you must always rename them!
The texture files, .shader file, and shader definitions inside the .shader file must all be renamed. Otherwise they can override the officially packaged versions, which usually results in missing texture errors on other maps.
Adding your username to the shader or texture name works well as this will usually be unique.
Also, only include shader definitions and textures that you have modified (and renamed). Including unmodified shaders will work initially, but eventually the official versions will be updated in a new Xonotic version, and then things will break. For example, several old maps included complete copies of common.shader, which breaks warpzones in current Xonotic versions.