I'll post the answer here in case anyone comes into it...
You can only get this event once for when the bot was added to the team. If you miss it, you no longer get the data. Uninstalling and reinstalling the bot will not fire the event again. If you're still not getting it, the recommended action was to remove the app from Azure and re-do it with the same name.
See more on the github discussion
In our scenario, I decided that the limitations on this were not within the realm of what I considered a working solution and I decided to go down a different route for getting the team data. Since the data was coming through in events after this one, I grab it then and do what I need to do with it.
