Troubleshooting Missing Mixpanel Session Events in Unity SDK

Hi all, i have just started using Mixpanel unity SDK with our mobile game in production. i understand that $session_start/end are virtual events that are created by Mixpanel. but i have yet to see them in any reports or the events tab, even though more than 24 past since we launched. all other events are working fine and as expected. our project settings is using the default session parameters, which is time based, 30 minutes. any idea what i am missing?