Note: I’m not talking about general stuttering and hitches in Forza Horizon 4. I would imagine if you aren’t rocking an Xbox One X this is par for the course. At least, this has been my experience.
After installing today’s update for Forza Horizon 4 (October 11, 2018), I initially booted to terrible performance and low FPS. I’m using a base Xbox One for reference, but I thought I’d let others know what I did if anyone else out there runs into this with the current or any future updates (restart your Xbox One).