Per an article ~2 years ago Mahershala had been asking for script changes. No question that as an actor Mahershala is fantastic. Additionally I expect as an actor he can recognize when a script isn’t going to work.

Now he isn’t a writer, so it’s possible his suggested changes just made things worse. Knowing something isn’t working and fixing something that isn’t working are two different tasks. It’s also possible it just isn’t fixable.

It sounds to me like the film is probably back to the drawing board and Mahershala, while still attached, will have an option to exit once the new script is written.

It’s also possible that the film has been scrapped completely, but Disney isn’t ready to announce it just yet. I think that’s less likely, but possible.