00:00:04.421 Publishing build last changes...
00:00:04.422 ERROR: Last Changes NOT published due to the following error: Could not find previous head of repository located at /var/lib/jenkins/jobs/omni-pipeline/branches/release-3-8.d1f6no/builds/28/.git. Its your first commit?
The lastChangesPlugin appears to be looking for ".git" in jobs/.../branches/.../builds rather than in workspace. This was with vcsDir: ''. I've additionally tried providing it hints via a more explicit vcsDir, but it still seems to go looking in jobs directory.