pt-heartbeat showing "Host is blocked because of many connection errors"...but connections are well under limit

I'm running MySQL in a master-slave configuration. pt-heartbeat is showing "Host is blocked because of many connection errors"...but connections are well under limit (limit is 600 connections, MySQL workbench shows I'm hovering around 250, and I'm having no other problems connecting).

Here is my CLI, running from the master:

PTDEBUG=1 pt-heartbeat --host="mysql-slave" --user=root --ask-pass --database="percona" --monitor --master-server-id="14"

Any ideas? Should I run the suggested 'mysqladmin flush-hosts' as PTDEBUG suggests? I just don't feel that's the problem if I'm below the limit and not seeing this anywhere else.

Thx