Deleting your DerivedDataCache folder of your project should force the editor to compile -> How to Force Shader recompile of everything like the first time you run the engine? - General Discussion - Unreal Engine Forums
Shader caching and cooking
Once shaders are compiled, they are stored in the Derived Data Cache. They contain, in their key, a hash of all the inputs to the compile, including shader source files. That means that changes to shader source files are automatically picked up every time you re-launch the engine or do a ‘recompileshaders changed’.
When you are modifying FShader Serialize functions, there is no need to handle backward compatibility, just add a space to a shader file that is included by that shader.
When cooking assets, material shaders are inlined into the material’s package, and global shaders are stored seperately in a global shader file which allows them to be loaded early in the engine startup.