On Aug. 2nd, the Orbit app received an unexpected error from the Twitter API which caused several Twitter integrations to be marked as invalid. As a result, we stopped importing new activities for these integrations.
The bug was fixed on Aug. 12 and activities are now being successfully imported.
If the Twitter integration in your workspace has been affected, you may see a big spike in new members on Aug. 12 due to the activities import adding new members from the past 10 days.