Create Blueprint Interface and assign it an Input variable pin of type “Material Interface - Object Reference” (it’s possible this happens to other stuff too)
Then create a Blueprint Actor Component that uses the Interface and calls it’s message while inputting own variable pin of type “Material Interface - Object Reference” into the Interface Message node.
Compile.
Compiler says "No value will be returned by reference. Parameter ‘NewParam’. Node: "
I’ve followed your repro steps in UE 4.17 but unfortunately I was not able to get the "No value will be returned by reference. Parameter ‘NewParam’. Node: " message when compiling. The compile was successful when I tried it.
Would you mind providing us with a small test project so that we can investigate the issue further?