What triggers this to start happening? How do we make it happen to investigate it?
The FTP Log window may indicate what is being done with the connection, which may in turn help understand why it is reconnecting (or at least why Opus wants the connection at all; the reconnection part may be because the site keeps dropping the connection).
Another thing to check is that other FTP clients don't have similar problems when doing the same sort of thing on the same site, and that they & Opus are configured the same (PASV mode etc.).