I am having this same problem, people think they unsubscribe, because they end up on the confirm page, but when I check that lead, unsubscribed is unmarked.
Set up a dummy record and try to unsubscribe on your forms. Take a look at that dummy record activity history see if there is any data changes taken place or delays that could give you some insight as to why your leads are not unsubscribing. You should see if the if the unsubscribe token is working correctly or not.