Forget does not completely delete the client. What it does is hide the client's name from view and in the background it anonymises the data associated with it at a later time. We found this out as if you forget a client that is blocked, the client remains blocked. You have to wait until the Meraki dashboard learns the client again (you cannot manually create the client by MAC as it still associates the hidden forgotten one in preference) and then you can set a policy.
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