Have you used "git bisect"?

Just reading up on it now. Seems interesting, might give it a shot next time.

In the case you mentioned of "just a few commits" it's of marginal utility, because you can do that manually almost as quickly, but it's a killer when it comes to "I don't really know when we introduced this" and you have to sift over thousands of commits. Unfortunately, it requires that you have the discipline to keep every commit on the relevant branches buildable (enough so to find the bugs), which is something you can do going forward but can't retroactively apply to a code base very well.

Agreed. Bisecting a deep and complex version history can be a lifesaver, especially under a time crunch.

Fossil has bisecting with much the same CLI as Git, for what that's worth.