Hi There looks like a bug, no directory http://ftp.freebsd.org/pub/FreeBSD/snapshots/ISO-IMAGES/11.0/ meanwhile http://ftp.freebsd.org/pub/FreeBSD/snapshots/ISO-IMAGES/12.0/ exists. not all mirrors have this, for example http://ftp.se.freebsd.org/pub/FreeBSD/snapshots/ISO-IMAGES/11.0/ - looks fine.
Closing as "Overcome by events" since all 3 links return 404 now.