This error occurs since some days.
# LANG=C less /etc/apt/sources.list.d/siduction.list
deb http://ftp.spline.de/pub/siduction/extra unstable main
deb http://packages.siduction.org/extra experimental main contrib non-free
deb http://ftp.spline.de/pub/siduction/fixes unstable main contrib non-free
# LANG=C apt update
...
Err:1 http://ftp.spline.de/pub/siduction/extra unstable InRelease
Could not connect to ftp.spline.de:80 (130.133.110.66). - connect (113: No route to host)
Err:2 http://ftp.spline.de/pub/siduction/fixes unstable InRelease
Unable to connect to ftp.spline.de:http:
...
W: Failed to fetch http://ftp.spline.de/pub/siduction/extra/dists/unstable/InRelease Could not connect to ftp.spline.de:80 (130.133.110.66). - connect (113: No route to host)
W: Failed to fetch http://ftp.spline.de/pub/siduction/fixes/dists/unstable/InRelease Unable to connect to ftp.spline.de:http:
W: Some index files failed to download. They have been ignored, or old ones used instead.