With HTTP::OAI 4.x, any request to oai.pl will fail with the following error: Can't locate object method "xslt" via package "Koha::OAI::Server::<package>" at /home/koha/koha/Koha/OAI/Server/Repository.pm line 147. libhttp-oai-perl 4.03 is included in Debian 9 (stretch) and Ubuntu 16.04 LTS (xenial). It means that the OAI-PMH webservice does not work on stable distributions (unless an older version is installed using cpan) Koha should be updated to work with HTTP::OAI 4.x
*** This bug has been marked as a duplicate of bug 17704 ***