After updating an application group with an updated list of whitelisted/blacklisted apps, the changes do not take place on devices.
Making changes to an app group alone will not automatically push the changes to corresponding devices. Upon making changes to an app group, the corresponding profile must be re-published for the changes to be applied to the corresponding devices.
Another important aspect to review is which organization groups have been assigned the blacklist app group. The blacklist app group must also be assigned appropriately before it can be used within an application control profile.