Security Group Questions

Is there a reason why a listview will display records if a user belongs to the same group as another user but not the group that the record belongs too?

That all depends on the roles being applied to the logged in user. If a user isn’t seeing the records in a list view even if the user’s group(s) are assigned to the records then there is some role being applied to the user that is set to Owner or None instead of Group or All. You can view how all roles are being applied to a user by going to the user record and clicking on the Access tab.