Given this can be reproduced on other machines with Cygwin and MSYS2, and that there is a (smaller) performance shift for Strawberry Perl from 5.20, this is probably worth reporting to p5p.

There was another regex related issue posted here late last year in 11153747 which was reported and fixed under https://github.com/Perl/perl5/issues/21360. It manifested in 5.28 so a different cause is likely, but the GH issue includes some debugging steps that could be followed if people have the tools, time and inclination.