apt update - could not connect

I use Ubuntu 20.04.2, fresh install. I have a /29 public network x.x.x.80/29

When I set my IP to x.x.x.83 everything works fine. As soon I set my IP to x.x.x.82 I can not use apt update.

Here the error:

apt update Err:1 http://ch.archive.ubuntu.com/ubuntu focal InRelease Could not connect to ch.archive.ubuntu.com:80 (2001:1620::1620), connection timed out Could not connect to ch.archive.ubuntu.com:80 (109.202.202.202), connection timed out

I also tried to change the archive to de.archive.ubuntu.com - same situation

But traceroute ch.archive.ubuntu.com works:

Has anyone an idea how to fix that?