I was in the process of testing and I think I broke the website. Most likely a database restart should fix the issue.
What I did:
1. Schedule a content object for publishing in the future
2. When back again to the same content object (prior to the publish time) and clicked on ‘Discard changes’
3. On the dashboard, I got an error (please refer to the attached image)
After this I have not been able to schedule any other content object for future publishing.