When visiting http://discourse.example.com/admin/groups/custom …
The group total shown I think is either the all-time number of members to join the group or the peak number of members to be in the group. It’s not the current number of members in the group though:
After you click the group, the number changes to show the actual number of users currently in the group:
It’s a very minor bug, but it does throw me off from time to time!