Cyrus-IMAP and Cyrus-SASL have been using a custom manpage generator, rather than the one built into Sphinx. But that custom generator is unmaintained, and keeps breaking when new Sphinx versions are released.
Cyrus-IMAP have retired the custom generator as of a few weeks ago, and we now just use the manpage generator that comes with Sphinx. It seems to do the same job -- I don't know why we had a custom one in the first place.
I've opened a PR to make the equivalent changes to Cyrus-SASL: https://github.com/cyrusimap/cyrus-sasl/pull/796. It works for me, but ought to be tested by someone who publishes Cyrus-SASL releases, as that's who it ultimately needs to work for.
I've requested a review from Quanah, but I'm not sure who else to request one from. I'm not sure if this project makes much use of the PR review process, and maybe the review request has simply gone unnoticed, so I thought I'd mention it on the list too just in case.