Does your video card driver up to date?
It's a quirk of the Stellar Forge. Galaxy is made of these (IIRC) 1000 Ly * 1000 Ly * 1000 Ly cubes which have all a star density parameter. You're seeing the boundary of 2 cubes.
This is a long-standing issue with background generation near the core, nothing wrong with your system.
Does your video card driver up to date?