Comment by emmelaich

I think it's not uncommon. I've seen it in two places recently.

1. A test job in CI/CD pipeline suddenly taking a very long time and lots of cpu

2. A data cleansing / checking job in a Java webapp occasionally turning the machine to molasses.

In both occurrences the regex had been around for a while; what happened is that the data was different. e.g. Lots of trailing whitespace.