Marketing Cloud Group contains more Subscribers than meet criteria

A very common reason for this behavior is that some Subscribers will unsubscribe while they exist in a Group. When this happens, these Subscribers will remain in the Group indefinitely regardless of if they currently meet the criteria for said Group.

For commercial sends, these Subscribers will not be sent to due to this status. If this does not meet your use case requirements, recreating the Group will only bring in the Subscribers that meet the Group criteria.  If you would like this behavior to no longer happen moving to Data Filters/Query Activities would be a way to avoid having this occur again.