Okay, maybe I've been living under a rock, and I haven't been building workflows in the last few months as I've been working on another project.
However, I have been working on a workflow today, and it's bitten me twice today. In n8n 2.0 they introduced a new workflow paradigm. Saving a workflow saves your changes as drafts and does not update production, but you have to republish it for those changes to go live in production.
I've been fighting all day to get this workflow to work correctly, and both times it came down to this issue.