You may notice that you have received an email notification about content from your community. However, when you visit the related content, you don't see yourself tagged or see another user tagged. This article explains the possible reason for this behavior.
There can be two possible reasons for this behavior based on the email's subject line,
If the email that you have received has the subject You have been mentioned, then the author must have edited their content (post, document, comment, etc.) to remove or replace the tagged user. Content editing doesn't generate email notifications, hence you will not get another email notification when the content has changed and you will also not see the expected username in the content.
For any other subject line in the email, you have received the email about the content because you are following the content in the Jive community, and not because of the @mention feature.
Both of these cases are a part of Jive's functionality and they are working as expected.