With a cast of heavyweights like Thandie Newton, Donald Glover, and Emilia Clarke, I have trouble believing that acting is the trouble. Not to mention that reshoots would solve that particular problem relatively quickly. If I had to guess, Lord and Miller had a different idea for what the film's tone should be than what Disney executives probably wanted. Regardless, Rogue One had a bit of a troubled production and that film turned out fine. I suspect the same will go for this movie.