When using FTP I noticed rather often a growing tree in the file display with parts of the structure appearing multiple times. I used to think this is a mere cosmetic problem caused by the ancient protocol, but now I ran into problems because Opus wanted to operate on files that don't exist, at least not in this part of the tree. I turned the FTP server off and on and refreshed Opus several times, but I needed to wait rather long to see the correct file list.
I checked with FileZilla and didn't see any of the problems, so I guess the FTP server is ok and the problem is more likely located on the Opus side.
The folder in FileZilla:
... and in Opus:
Ghost folders even after turning the FTP server off:
The FTP site configuration in Opus is a standard connection and everything default.