[Koha] OPACXSLDetailsDisplay - No display at all in OPAC

Hi everybody, It's my first message on this list. I hope that I'm using it properly. Since the upgrade of my installation of Koha to version 20.11.11.000, I have the following issue. If I change the settings of OPACXSLTDetailsDisplay system property to /usr/share/koha/opac/htdocs/opac-tmpl/bootstrap/en/xslt/UNIMARCslim2OPACDetail.xsl and of OPACXSLTResultsDisplay to /usr/share/koha/opac/htdocs/opac-tmpl/bootstrap/en/xslt/UNIMARCslim2OPACDetail.xsl, I get an *empty display without any data*, as if Koha ignores completely the xsl transformation and returns *nothing to display*. Koha ignores completely the directives in this XSL file. There is probably something I've completely forgotten. Any help would be appreciated! Rémi