apt-get update stuck: Connecting to security.ubuntu.com

When I run apt-get update on my machine it gets stuck at:

100% [Connecting to security.ubuntu.com (2001:67c:1562::15)] [Connecting to archive.canonical.com (2001:67c:1360:8c01::16)]

I have made no recent changes to the system and use my home network which worked fine previously.

I can't explain why it switched to using IPv6.
I have IPv6 set to ignore for the wireless network:

Ouput of ip addr:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default 
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
   valid_lft forever preferred_lft forever
inet6 ::1/128 scope host 
   valid_lft forever preferred_lft forever
2: mlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
link/ether 4c:0b:be:22:0a:b4 brd ff:ff:ff:ff:ff:ff
inet 192.168.2.106/24 brd 192.168.2.255 scope global dynamic mlan0
   valid_lft 1814086sec preferred_lft 1814086sec
inet6 ::d5:b551:28db:2789:225/64 scope global temporary dynamic 
   valid_lft 604483sec preferred_lft 85483sec
inet6 ::d5:4e0b:beff:fe22:ab4/64 scope global mngtmpaddr dynamic 
   valid_lft 604779sec preferred_lft 86379sec
inet6 fe80::4e0b:beff:fe22:ab4/64 scope link 
   valid_lft forever preferred_lft forever

This worked for me, courtesy of Zach Adams (https://zach-adams.com/2015/01/apt-get-cant-connect-to-security-ubuntu-fix/):

Turns out this is an issue where connecting over IPv6 on some servers causes them to get stuck at this point. The fix is really simple.

Open /etc/gai.conf

Under the line

# For sites which prefer IPv4 connections change the last line to

Uncomment the following line by removing the #:

# precedence ::ffff:0:0/96 100

This will allow you to still use IPv6 but sets IPv4 as the precedence so that apt-get won’t get stuck.

The IPv6 setting for the network were ignored, but disabling IPv6 via /etc/sysctl.conf worked:

Add the following lines at the bottom of /etc/sysctl.conf:

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

Run sudo sysctl -p to reload the /etc/sysctl.conf settings.