Comment by Aqwis

Sounds like a process similar to how you would debug a difficult bug in a big and/or complicated codebase – through trying to isolate the code causing the bug, comparing the buggy code with code that's known to work, replacing other parts of the code with dummy code/mocks etc. And sometimes a bug seems impossible to solve regardless of how much developer time you throw at it, and you just have to ship the product with the bug (seems to be especially common in the game dev business).