When you see No services selected on your Scheduled or Sent messages, this means that the Service/s or List you added to the message were deleted after the post was created, therefore there is no Service or List selected for the message to be sent to.
1. If you click on the Edit logo on the right side of the post in your Scheduled view you can re-add a service and make any other updates to that post that you need to.
Once the scheduled date on the post has passed, if the post was not updated to include services for the post to be sent to, it will go to your Sent view, even though the post has not been sent out.
2. You can still Repost the message to a new service from your Sent view by selecting the Repost icon and updating the post as needed before rescheduling.