/./ is often assumed to mean "any character", but doesn't match new lines. Conversely, it could have been meant as a literal "." rather than the meta character it is in patterns. Particularly where IP address or domain names are involved.

Unanchored patterns is another problem /10\.0\.0\./ will match "110.0.0.0", for example.

I'm not sure how using common problems is going to be of use as a gauge for debugging skills. I would have red-flagged those instances even before starting to debug.