Kia ora, greetings -- from the past, some of you will remember me. Nut shell : we have been running (charitable library, non lending) Koha catalogue since 2011 (v. 3.08.24 since July 2015). Rock solid until we got overwhelmed by DDoS and/or AI bots. Thermal protection on the Koha server (apache2 proxied from nginx) failed, literal meltdown. Built a new server (12 core intel CPU, 64G memory, Ubuntu 14.04 LTS security mods - I know, please don't flame me), reinstalled from tar and backup. Apparently a dead-ringer copy of what we had for over a decade. Public server perfect <https://opac.navalmarinearchive.com>. Mysql, Zebra, Pazpar have reconstituted over a hundred thousand biblios and items - no discernible errors, all public users happy (except hackers and AI bots mitigated at front end nginx.) But ... Koha admin (intranet) works fine for everything (items, reports, logs, "about"...) EXCEPT Biblios won't edit nor write new (manual input, nor z3950) records. ERROR : Can't call method "fields" on an undefined value at /usr/share/koha/lib/C4/Biblio.pm line 2483. 2482 # traverse through record 2483 MARCFIELD: foreach my $field ( $record->fields() ) { 2484 my $tag = $field->tag(); if elsif .... We've spent nearly a week, finding minor variations in backups of Biblio.pm (occasional line renumbering and developers' signatures), nothing from a Perl logic perspective. We've done the obvious "diff's", permissions, ownerships, restarts, reboots, koha_perl_deps.pl, SAX parser, perl modules, environment. It's got to be something blazingly simple, after a decade of superb Koha service. Any and all assistance in saving my sanity would be truly appreciated, Thanks and warmest regards, Paul