Hi @julien
I’ve managed to install Tutor on Ubuntu 20.0.4 without issue, I’m unable to replicate your problem which leads me to believe it’s most likely connectivity related (this does not automatically mean YOUR internet is bad, just that something in the route is bad)
I figured out though that the Debian sources are most likely coming from one of Tutor’s containers, rather than the base OS.
This might function as a workaround, try force it to use a specific IP address for {deb|security}.debian.org by creating a hosts entry on your server
sudo nano /etc/hosts
create a new line with an alternate IP address and deb.debian.org and security.debian.org
127.0.0.1 localhost
127.0.1.1 tutortestvm
45.125.0.6 deb.debian.org security.debian.org
Here are some alternative IP’s you could possibly try:
78.129.164.123 (UK)
64.50.236.52 (USA)
208.80.154.139 (USA alt)
64.50.233.100 (USA alt)
140.110.240.80 (Taiwan)
103.84.224.37 (Australia)
Some testing I’ve done indicate that it should work for the docker containers to resolve the new IP address instead of the “geographically closer” one that deb.debian.org typically resolves to. If there is another mirror that you prefer to use then put that mirror’s IP address (eg mirrors.tuna.tsinghua.edu.cn which you were using here is 101.6.15.130)