fgrep excessive time increase after upgrade from 12.4 to 14.3 – regex library issue?

This is a weird one. Since upgrading FreeBSD (jumping a couple of major versions), a script that used to run in less than a minute now takes literal hours. I’ve managed to distill the delay down to this use of fgrep:

cat filename.txt | fgrep --text -if filter.txt

– filename.txt contains 64 million lines, 2.4 GB
– filter.txt contains 615 lines, 6 KB

fgrep CPU usage is at 100% consistently.

I do have a backup of the 12 system, and I did notice one possible explanation:

fgrep 12.4: libgnuregex.so.5
fgrep 14.3: libregex.so.1

I cannot find any information about this change, or anyone else mentioning a regression. Hope someone has some insight. Thanks.