Hello,
I just tried it out myself on a new tenant. Repro:
1. create two new sandboxes (v19.0)
2. create two security group and add a few members to these new security groups
3. logon to one of the BC tenants
4. process new user (all users are added despite to what SG they were added to)
5. try to logon to a BC tenant with a user that is not assigned to the SG that has access to the resource
Result:
We do not recognize you. Did you enter your credentials correctly?
You do not have access to this environment. You must be a member of a security group that is associated with the tenant. Please contact your system administrator.
Date and Time: 2021-11-08T09:17:07.327Z
AAD tenant ID: <<removed>>
Operation ID: 435dd6de-f198-47e7-b73d-a2e4be58cfa0
There is no longer a need to logon to the tenant and disable the users that should not have access to the production environment.
Hope it helps.