Koha z39.50 MARC record import fails

Koha is a fantastic open source product. Huge libraries run on it.

We suddenly (possibly after an upgrade) started getting first this error:

All arguments must be MARC::Field objects at /usr/share/koha/intranet/cgi-​bin/cataloguing/addbiblio.pl line 151

And then suddenly this one:

Can't call method "add_subfields" on an undefined value at /usr/___/cataloguing/addbiblio.pl line 142

This was resolved after days of hell by finding the solution to the second error here:

Resolve the error by changing the "z3950NormalizeAuthor z3950AuthorAuthFields" setting under the Cataloguing Tab, and Record Structure section to "don't copy".