... on my computer:
# LANG=C apt update
Ign:1 http://ftp.spline.de/pub/siduction/extra unstable InRelease
Ign:2 http://ftp.spline.de/pub/siduction/fixes unstable InRelease
Err:3 http://ftp.spline.de/pub/siduction/extra unstable Release
Unable to connect to ftp.spline.de:http:
Err:4 http://ftp.spline.de/pub/siduction/fixes unstable Release
Unable to connect to ftp.spline.de:http:
Hit:5 http://download.virtualbox.org/virtualbox/debian jessie InRelease
Hit:6 http://repository.spotify.com stable InRelease
Hit:7 http://mirror.sinavps.ch/debian testing InRelease
Hit:9 http://debian.ethz.ch/debian experimental InRelease
Hit:8 http://ftp.nl.debian.org/debian unstable InRelease
Hit:10 https://deb.opera.com/opera-developer stable InRelease
Hit:11 http://incoming.debian.org/debian-buildd buildd-unstable InRelease
Reading package lists... Done
E: The repository 'http://ftp.spline.de/pub/siduction/extra unstable Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure( manpage for repository creation and user configuration details.
E: The repository 'http://ftp.spline.de/pub/siduction/fixes unstable Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure( manpage for repository creation and user configuration details.
Certainly no local router problem.
Update1:
Not accessible by mobile network.
Update2:
spline server accessible again.