[Koha] OPAC Search results - 500 Error

[John J. English]

Hello all, I'm having trouble getting detail for books in the OPAC.
If I search for something in the catalog I'm presented with ta list of books. 
If I click the title of a book I get a 500 error. I think it must something to do with "DBIC result _type  isn't of the _type Branch" seen in the plack error log. 
Relevant logs are below. Any help is much appreciated. Thank you.


==> /var/log/koha/library/plack-opac-error.log <==
[2023/04/18 11:06:04] [WARN] Use of uninitialized value in hash element at /usr/share/koha/opac/cgi-bin/opac/opac-detail.pl line 680.

==> /var/log/koha/library/plack-error.log <==
DBIC result _type  isn't of the _type Branch at /usr/share/koha/opac/cgi-bin/opac/opac-detail.pl line 680.

==> /var/log/koha/library/plack.log <==
192.168.101.254 - - [18/Apr/2023:11:06:04 -0600] "GET /opac/opac-detail.pl?biblionumber=631&query_desc=kw%2Cwrdl%3A%20deep%20work HTTP/1.1" 500 20863 "https://library.ncat.org/cgi-bin/koha/opac-search.pl?idx=kw&q=deep%20work&sort_by=relevance_dsc&count=20&limit=holdingbranch:MT" "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/112.0"

==> /var/log/koha/library/opac-access.log <==
192.168.101.254 - - [18/Apr/2023:11:06:04 -0600] "GET /cgi-bin/koha/opac-detail.pl?biblionumber=631&query_desc=kw%2Cwrdl%3A%20deep%20work HTTP/1.1" 500 20863


JOHN J. ENGLISH