Hello PhroZenOne,
I’m currently looking into this for you. I’m not familiar with this specifier as of yet so I’ll need to look into that but just from comparing your setup to some in the engine such as the declaration for GetStructFromBox in StructBoxLibrary.h in the engine, I can see that the UFunction declaration and the DECLARE_FUNCTION parts are in the .h for the class while your gist is listed as being in the .cpp. Could this be related to the problem as it seems like a possible parsing/include issue?
I also see that this example one uses the following line for its variables that are being passed in by reference, although I’m not sure that omitting that would cause this behavior.
PARAM_PASSED_BY_REF(StructBox, UStructProperty, FStructBox);