I use namespaces to organize my assemblies. It seems that Netcode is incapable to generate source for Ghost components or rpcs that are in a custom namespace?
NetCodeSourceGenerator\Unity.NetCode.Generators.NetCodeSourceGenerator\W15.Components\GhostComponentSerializerCollection.cs(34,64): error CS0234: The type or namespace name 'Gameplay' does not exist in the namespace 'W15.Components' (are you missing an assembly reference?)
Strangely enough, it seems to work for the Megacity-Metro sample?