Mixpanel Session Tracking Issues with Segment Implementation

Help! We’ve recently implemented Mixpanel with Segment. As far as I understand, session start, session end, and session duration are automatically calculated by Mixpanel, but all of these appear as (not set). I’ve been looking through the documentation but I can’t find anything to explain why I don’t have these values that should be being tracked by Mixpanel out of the box. Maybe it has to do with our Segment implementation but I’m stumped 🤔 Any help would be appreciated! (Note: We have Sessions defined as Timeout Based (30 minutes) in the Project settings)