FTP access autoblocked - black listed

My Ftp client’s schedule task get always autoblocked after a couple of week or days.
In the menu settings -> network ->ftp configure -> next -> next…and it s listed in “blocked ip”.
I have to manually delete it to get my ftp client back on track.
I ve got the last update of the firmware and the default ftp settings

. It sounds like a time out issue.