Bug - connected with that user already confirm his email address

I think there is a bug, when subscriber unsubscribe from list, and after that try to subscribe again to the same list phplist sent confirmation email, but after clicking on it says that confirmation has been already sent.

phplist 3.0.12

You are correct, but it is caused by the same underlying problem in phplist as caused your other topic on the invite plugin.
The next release of phplist,3.0.13, should fix that problem.

Cool Discourse feature, if you paste the url of the other topic Invite plugin - CONFIRMATIONURL doesn't work it creates a navigation link on the right hand side - of both posts!