Has shown up in the pulpcore 3.16 repo. Is this inadvertent? I experienced a number of problems with content update tasks including missing column errors, which would be consistent with a mismatched version - I downgraded to the 3.16 version and these problems went away.
pulp_rpm 3.17.3 is compatible with pulpcore>=3.16.0,<3.20, so there is nothing inherently wrong with it “appearing” in the pulpcore 3.16 repo. However, if you upgrade to it, I expect you then need to apply any new migrations using pulpcore-manager migrate. Not doing this (for example by running only yum update) would cause the kind of errors you describe.
Another question I don’t know the answer to, is whether Katello has the right Ruby bindings gem to speak to this new version of pulp_rpm. Perhaps someone else can weigh in on this?
I spoke to some more people and received the following additional information:
One should never update any Foreman/Katello/Pulp packages on a Katello installation, without also running the foreman-installer (which will run pulpcore-manager migrate amongst other things).
If a new Pulp plugin version is available, then that plugin version has been tested against the Ruby bindings used by Katello, so this should never be an issue.