Hey. I was able to recreate the error somewhat. Let me know if this was the problem you were facing.
- Launched both Unreal Engine and VS.
- Added the function to C++ and compiled with live coding
- Override the C++ function and It worked
- Closed Unreal engine
- Open Unreal Engine
- Open Blueprint and function was producing the error
If this is the case, you have to build the project from C++ as some VS files for unreal engine might not be generated when using live coding. I hope that helps.