Connect to your box with a sftp client for Windows like WinSCP or Filezila Client create a file outside the mount folder, then try to move it to inside, you’ll fail.
I think this is really annoying and makes working with a mount folder locally difficult. I’ve found that the mv command works.
Just mount a rclone with google drive, connect to it with WinSCP, try to move files using drag and drop to and outside a folder inside the mount. It will fail with error 4.
I’m having the same issues, works when moved or renamed locally, or via a samba share. Just doesn’t work when using sftp clients (I’ve tried two and the same issues exist in both).