CiviRules not triggering event reached date
I think the issue would indeed be that there are no participants, so therefore no events joined and an empty start_date. Can you try with a participant?
If the issue persists can you please report it as a bug on the Civirules extension page (https://lab.civicrm.org/extensions?utf8=%E2%9C%93&amp;filter=civirules)? Would fixing it be possible for you?