This may be happening due to one of the reasons mentioned below:

• You may be facing this problem if you are trying to add more than 20 tags. We have a limit of 20 tags per presentation. In case, you add more than 20 tags, they would be discarded by our system.

• On the presentation view page, we show only the top 25 tags which are a combination of author’s tags and community’s tags. So if the presentation has a large number of tags, the others (beyond 25) will not be displayed.
• If neither of the above two reasons are true, this is likely happening due to page caching.  We request you to wait for a few minutes and your tags should show up.