Race condition

A race condition is the term often used to describe bugs which are hard to reproduce reliably because they are timing dependent.

The bug only shows up when A happens before B and much of the time B happens before A.

So these bugs are by their nature difficult to reproduce. The good news is they are also hard for customers to reproduce so when it comes to prioritization it’s not the worst thing in the world to fix the easily reproduce-able bugs - that clears the windscreen makes it easier to find the remaining difficult to reproduce bugs like race conditions.