Under "No Access",  options are either unchecked or disabled.

Please navigate to Forum Accesses and Check "No Access" all the options must be unchecked/disabled.

When a member subscribes to all topics and posts for all forums using the Subscription Manager,  that member also gets notification emails for the forums that he does not have access to.

I have a forum to which i have given No Access to everybody and Standard Access to only one usergroup.  But few members who are in the "No Access" usergroup and who have subscribed to all the forums under the Subscription Manager are getting notification emails whenever a topic or post is created in that forum.

I have noticed whenver the itemId is "0" in the wpforo_subscribes table, this problem happens.  If they uncheck just one forum its okay.   Just to be clear , the forum that should not be visible to them is NOT seen under the subscription Manager, so thats also good.