Updates on Jessie repos failing

[Vinzenz Vietzke]

Wheezy and Jessie were recently removed from the mirror network, so if you want to continue fetching Jessie backports, you need to use archive.debian.org instead. The same applies to jessie-updates.

Furthermore Acquire::Check-Valid-Until "false"; needs to be set or applied via -o parameter. Otherwise apt update will fail.

(Source: https://unix.stackexchange.com/questions/508724/failed-to-fetch-jessie-backports-repository)