There are two reasons why an automated message would send to 0 contacts.
- The Automated Message Group is using a query and the data in the database does not match.
- An import has not happened in the expected manner.
In regard to item 1, the easiest action is to check that you have contacts who meet the criteria prior to the schedule. You can do this by running a query or a copy of a query some time prior to the schedule. If you are importing data, view the data prior to the import if possible.
In regard to item 2, be mindful of your data jobs. Recurring import jobs can fail if the data has not fully uploaded prior to the schedule time, or if the file name does not match what is set in the Recurring Import settings.