This will happen if:
The My Agenda component in your attendee app includes Presentations;
The attendee has a “Session Role” (either author/presenter or co-author, or a Session Role you’ve created in the Presentations module, such as “Discussion Moderator” – see image below);
ANDThat session contains multiple presentations.
A person with a Session Role you’ve created will see ALL presentations in that session.
A presentation author/co-author will see multiple session listings if they’re attached to multiple presentations as an author/co-author. [For example, they’ll see the session listed twice if they’re an author/co-author on two different presentations.]
This is intentional, so that anyone with a session role can see any other presentations linked to that session.
Although initially the session names appear to be the same, clicking on each of them will display the different details for each presentation.