If you are pushing a playlist as an XML feed to podcasting apps, you may see published items not appearing.
Changes to XML feeds can take up to 10 minutes to be implemented. So changes in Platform may not be instantly apparent.
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'.
It is also worth checking publish dates on the item in question to ensure it hasn't unpublished itself.