Last tested: Nov 23, 2020
This often comes up on dashboards-next. This error will come up when some part of the validation of the schedule failed. This could be a schedule that was configured to do something the user didn't have permission to do, or send in a format not allowed.
If you see this error open up the dev tools network tab, click on the erroring request with the 422 response, and click on the "Preview" tab. This will hopefully have an error message for what went wrong, which might lead you to a solution.