I think I maybe solved the issue? I mean, its def a workaround lol but it can help MacOS users in the meantime -- original post on Naocat's thread regarding a similar issue on Mac RE: avatar not loading.
This method bypasses the need to press ESC (which throws that -50 error) and allows MacOS users to directly upload their asset folder to the corresponding AppData folder the program defaults to using. GLHF!