Thanks. I think I figured out the problem. Looks like their algorithm is seeing Opus listing all subfolders trying to get the folder sizes, and they probably detect some suspicious activity ending in auto-blacklisting my external IP address.
Hence another question, can I leave on auto folder sizing on all network folders and just leave-out the FTP folders?
Folder Formats can override that setting, if you need something more granular. You could turn if off in the FTP format, or turn it off globally and only turn it on for the folders or folder types you need it for.