Check the settings for that group, there may be an auto-add setting checked that defaults every new user to that group.  It below the area where you would manually add users.  

That was it. It was stuck on auto add for that unit. I really appreciate it. 

Side note - How would I add specific sub-groups into “auto-add”?  When I open most other groups the auto add feature is not even there.

That auto add feature should be there for all groups.  Another way to auto fill groups is by using job titles.  If you want specific job title(s) in a group, you can link the job titles to a group.  That way, when people move in and out of positions, they also automatically move in and out of groups.  If your permissions are tied to those groups rather than individuals, you don’t have to reassign permissions as people’s responsibilities and jobs change.

Thanks for the assist ​@Timothy.G15