Suppression list count increases with the reason "Unsubscribed from the Subscription Center" in Marketing Cloud
|Knowledge Article Number||000213979|
A Suppression List is a list of subscribers that you don't want to receive your communications. When you send an email to a Data Extension and you've selected a suppression list to exclude subscribers from receiving the email, any of the subscribers that aren't on the suppression list receive the email.
If one of the recipients clicks the "One-Click Unsubscribe" link in the email, they are unsubscribed from the list that the send originated from and are added to the suppression list. Even though it's not set to public, the suppression list count increases and shows the reason "Unsubscribed from Subscription Center" because they clicked the "One-Click Unsubscribe" link.