Debian 8 apt-get upgrade fails with Failed to fetch … Connection failed

Debian 8 "Jessie". CLI-only home-use server. apt-get upgrade always fails with E: Failed to fetch ... Connection failed ... errors. apt-get update appears to always succeed. Problem has been occurring for days. Upgrades were previously succeeding without issue. Recently re-sized the /home and /var drive partitions but cannot think of any other major changes. Have attempted to include several mirrors in /etc/apt/sources.list but none succeed. My sources.list file is:

deb http://mirror.it.ubc.ca/debian  jessie main
deb http://mirror.its.dal.ca/debian  jessie main
deb http://debian.mirror.iweb.ca/debian  jessie main
deb http://debian.mirror.rafal.ca/debian  jessie main
deb http://ftp3.nrc.ca/debian  jessie main

deb-src http://mirror.it.ubc.ca/debian  jessie main
deb-src http://mirror.its.dal.ca/debian  jessie main
deb-src http://debian.mirror.iweb.ca/debian  jessie main
deb-src http://debian.mirror.rafal.ca/debian  jessie main
deb-src http://ftp3.nrc.ca/debian  jessie main

deb http://mirror.it.ubc.ca/debian  jessie-updates main
deb http://mirror.its.dal.ca/debian  jessie-updates main
deb http://debian.mirror.iweb.ca/debian  jessie-updates main
deb http://debian.mirror.rafal.ca/debian  jessie-updates main
deb http://ftp3.nrc.ca/debian  jessie-updates main

deb-src http://mirror.it.ubc.ca/debian  jessie-updates main
deb-src http://mirror.its.dal.ca/debian  jessie-updates main
deb-src http://debian.mirror.iweb.ca/debian  jessie-updates main
deb-src http://debian.mirror.rafal.ca/debian  jessie-updates main
deb-src http://ftp3.nrc.ca/debian  jessie-updates main

Example of errors encountered:

Err http://mirror.its.dal.ca/debian/  jessie/main base-files amd64 8+deb8u2
  Connection failed [IP: 192.75.96.254 80]

E: Failed to fetch http://ftp3.nrc.ca/debian/pool/main/b/base-files/base-files_8+deb8u2_amd64.deb   Connection failed [IP: 132.246.2.23 80]

No proxy is defined in /etc/apt/apt.conf or /etc/apt/apt.conf.d Attempting to download the failed URLs on a different, desktop computer through a web browser also fail with connection errors. Perhaps related, attempting to download netinstall images with a desktop web browser from cdimage.debian.org always fail with a The connection was reset error. My Arch Linux desktop computer can upgrade packages fine.