Hey,
Yeah, unfortunately current rendering system is a bit problematic when creating complex surfaces like water. Had exact same problems when I was porting my ood ocean shader from UE3. What you can do is implementing your own shading model by setting lighting mode to unlit and enabling transparency. You will bypass all standard material parameters like roughness and implement your own params, specific to water shader. some standard nodes will not work, so you will need to create blueprint that will pass most important parameters to your material(light direction for example). Its a bit hacky way of achieving custom lighting models in UE4, but on the bright side, blueprints are so powerfull you should be able to bypass engine’s limitations.