I have a workflow 2013 that is set to start conditionally (simple prev value not equal to value). It stopped working without changes some days ago. I created a very simple test workflow on the same list and with the same start options and it doesn't work either. When set to start on changes without a condition it works perfect. A similar workflow on another list in the same site collection still works fine.
What could be the reason for the workflow not obeying the start condition anymore?