AWS Glue Job schedule missing

I have several scheduled Glue jobs, and now half of them have missing schedules. When I try to add a schedule back, a message in red flashes at the top of the browser, but the site refreshes to create schedule form again.

How do I find out what happened to the schedules, so they are not removed again, and how to I identify what is the error when adding a schedule back to the job?

Edit: Overnight, the schedule create failure has resolved itself. I was able to recreate the missing schedules. However, I need to know why the schedules were removed.