If you have an error that only occurs on your computer, on your compiler version, on your particular optimization level, on this particular phase of the moon, h

If you have an error that only occurs on your computer, on your compiler version, on your particular optimization level, on this particular phase of the moon, how do you determine that the root cause is forgetting to initialize a variable? In the context of debugging, "reproducible" means "can reproduce that exact error in order to better identify the root cause", not "frequently occurs as a root cause".