Host will be blocked when then number of interrupted connection attempt is more than the system variables of "max_connect_errors". In order to unblock the host, we may flush the hosts table in mysql database.
You may either flush hosts by mysqladmin:
mysqladmin -u username -ppassword flush-hosts
or by SQL:
To increase the "max_connect_errors", simply execute this:
Appreciate if you would like to share some guide on steps to troubleshoot the interrupted connect request. Thanks in advance.