Photo Library is Blank
When picking the Photo Library from the Saved Files tab, if FTP On The Go is showing blank, or a "working" progress bar that doesn't end...
This is caused by clicking to not allow access to "Location" data the first time the Photo Library folder was opened in FTP On The Go. Because your photos can have location infomation embedded within them, you must grant access to Location data for FTP On The Go to see the images.
Open the main Settings app.
Pick the General item, then the Reset item at the bottom.
Finally do the Reset Location Warnings.
Return to FTP On The Go, when you pick the Photo Library again, make sure you choose to allow access to location data.