Something certainly has changed, and it almost certainly is on your server, not the printer.
I'd wager that SMBv1 has been disabled, and with good reason.
The 6515 is fully certified to work via SMB2 and 3, so for it to fail for the above reason, I would assume the scan was setup using port 139, when it should be port 445.
As for the Discovery portion, I am looking into what may have caused that and will edit this post when I find something.