I am having the same issue in my project.
It was working fine but a couple of weeks ago start to fail.
It runs on a self-hosted machine.

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Also seeing this, but not self-hosted.

The CI job is "owned" by a person who is no longer with the company, so initially I thought this was part of the issue. However, we have another similar CI job owned by a different ex-employee and it's working fine.

Really annoying that this stuff is so opaque.

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these might be the related helpful issues :

1. Action suddenly not started with cron, saying (Unknown event)
   🔗 https://github.com/orgs/community/discussions/152481

2. Scheduled GitHub Action stops working if last committer deletes their account
   🔗 https://github.com/orgs/community/discussions/109354

3. New action triggering as unknown event - unnamed workflow
   🔗 https://github.com/orgs/community/discussions/25377

4. Cron problem (ox_lib inventory save issue)
   🔗 [Bug] Cron problem overextended/ox_lib#368

5. CronJobs always show Unknown error (404) the server could not find the requested resource
   🔗 CronJobs always show Unknown error (404) the server could not find the requested resource kubernetes/dashboard#7717

6. Scheduled Actions remains pending (not run automatically) in multisite
   🔗 Scheduled Actions remains pending (not run automatically) in multisite woocommerce/action-scheduler#740

7. Argo CronWorkflow unknown time zone issue
   🔗 Argo CronWorkflow unknown time zone  argoproj/argo-workflows#9091

8. Cannot be handled as a CronJob unknown field error
   🔗 cannot be handled as a CronJob unknown field  kubernetes-sigs/kubebuilder#3858

9. Argo cronworkflow showing a finished workflow under Active
   🔗 Argo cronworkflow showing a finished workflow under Active Workflows argoproj/argo-workflows#4181

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