CSG/Union lighting issue when slicing a cylinder

When I slice a cylinder, the lighting is messed up in the center point. This happen 100% of the time when i try to union negative part with a cylinder. It happen on both in-game and studio

This started happening after latest update (version 419).


Here is a rbxl file and the result not 100% same, but it happen all the time:
Bug report.rbxl (22.4 KB)

Other Information

  • CPU: AMD E-450
  • Ram: 2gb
  • GPU: AMD Radeon HD 6320 Graphics

Using your file I reproduced the same problem in studio.
Processor: Intel(R) Core™ i9-8950HK CPU @ 2.90GHz (12 CPUs), ~2.9GHz
Memory: 32768MB RAM
Card name: NVIDIA GeForce GTX 1080