When searching an authority from staff search, it returns Error: Unmatched [ in regex; marked by <-- HERE in m/^[ <-- HERE ]$/ at /usr/share/perl5/MARC/Field.pm line 643. the issue might stem from how the $subfields string is used in the regex within the conditional if statement. If $subfields contains special regex characters, especially an unmatched [, it could cause the regex engine to throw an error due to an invalid pattern.
This reads like this bug: Bug 35989 - Searching Geographic authorities generates error Maybe a duplicate?
yes it seems it is the same *** This bug has been marked as a duplicate of bug 35989 ***