Sometimes, through no fault of your own, tweets that you expect to be automatically pulled into an event, are not automatically pulled in. Here are some of the reasons why.
Is Twitter Down?
Once in a while, Twitter goes down. If Twitter is down, or experiencing intermittent issues, their API stops sending us tweets so no tweets will be added to your event. Check here to see if Twitter is down.
Is The User Excluded From Twitter Search
For reasons unknown, some Twitter users are excluded from Twitter's search results. If Tweets from a user aren't showing up, check that their tweets show up in Twitter's search results.
@ tweets not showing up?
When you follow a specific user or use Auto post, all @ tweets made in the beginning will not display. The idea being these @ tweets might be too specific to be useful to the overall event (like a comment). Retweets and @ tweets not in the beginning will display for specific users.