@Snatcher though I haven’t experienced the exact issue you mention, your note about this starting after you added C++ code makes me wonder if you have out of date build assets.
Try doing a full clean of your project. Remove all binaries and intermediates for the main project and all plugins. Then “Generate Visual Studio Project Files” again, and Rebuild your C++ entirely.
Sometimes when the combination of C++/Blueprints acts funky, this procedure solves it.