I’m using FOG 1.5.5 with init files included with it.
As suggested in a previous post (https://forums.fogproject.org/post/123192), I backed up init files stored in /var/www/html/fog/service/ipxe/ and put instead the last ini files.
I had the behavior described : shrinking OK but FTP error then. I put back the 1.5.5 ini files and then everything worked back. It’s may be just a coincidence I can try again.