What Causes Productivity to Go Down?

A really hard bug can drag productivity down, right? If there's like a super challenging issue that needs to be fixed, and it takes you two weeks to track it down, fix it and get it out in deployment. But then the question becomes, is that a productivity buster? I mean, if here was just a hard problem, s just a hard problems. Yesit n some people. Measuring the team make sense, because as a team, you gotto hav this has to flow.