If you are pushing a playlist as an rss feed to podcasting apps, you may see published items not appearing. 

Changes to RSS feeds can take up to 10 minutes to be implemented. So changes in Platform will not be instant.

If significant time has passed to no avail, you may want to check that your feed has validated. You can do this by clicking on the dropdown in the playlist's 'actions' column and selecting 'validate'.

Check your publish dates on the item in question to ensure it hasn't unpublished itself.