There are a lot of different questions around the bug with appstream-cli interfering with
apt-get update commands, with much varying titles.
appstreamcli hanging with 100% CPU usage during update
apt-get is stuck at "Fetched XXKb in XXsec"
Ubuntu 16 apt get update very slow / not working
Apt-get update hangs in 16.04
Should these all be marked as dupes, and is there a suitable question to link them all to?