There is something wrong with archive.ubuntu.com. But ru.archive.ubuntu.com works normally.

You can compare command outputs below:

```
http_proxy=http://192.168.3.222:8000 wget --server-response --no-cache -c http://archive.ubuntu.com/ubuntu/dists/focal-updates/main/dist-upgrader-all/current/focal.tar.gz
--2020-07-23 19:26:27--  http://archive.ubuntu.com/ubuntu/dists/focal-updates/main/dist-upgrader-all/current/focal.tar.gz
Connecting to 192.168.3.222:8000... connected.
Proxy request sent, awaiting response... 
  HTTP/1.1 416 Requested Range Not Satisfiable
  Date: Thu, 23 Jul 2020 16:26:27 GMT
  Server: Apache/2.4.29 (Ubuntu)
  Content-Type: text/html; charset=iso-8859-1
  X-Cache: MISS from squid-deb-proxy
  X-Cache-Lookup: HIT from squid-deb-proxy:8000
  Transfer-Encoding: chunked
  Via: 1.1 squid-deb-proxy (squid/3.4.8)
  Connection: keep-alive

    The file is already fully retrieved; nothing to do.

http_proxy=http://192.168.3.222:8000 wget --server-response -c http://archive.ubuntu.com/ubuntu/dists/focal-updates/main/dist-upgrader-all/current/focal.tar.gz
--2020-07-23 19:30:08--  http://archive.ubuntu.com/ubuntu/dists/focal-updates/main/dist-upgrader-all/current/focal.tar.gz
Connecting to 192.168.3.222:8000... connected.
Proxy request sent, awaiting response... 
  HTTP/1.1 200 OK
  Date: Thu, 23 Jul 2020 16:23:16 GMT
  Server: Apache/2.4.29 (Ubuntu)
  Last-Modified: Thu, 16 Jul 2020 08:58:10 GMT
  ETag: "1464d5-5aa8b3d596c80"
  Accept-Ranges: bytes
  Content-Length: 1336533
  Content-Type: application/x-gzip
  Age: 412
  X-Cache: HIT from squid-deb-proxy
  X-Cache-Lookup: HIT from squid-deb-proxy:8000
  Via: 1.1 squid-deb-proxy (squid/3.4.8)
  Connection: keep-alive

    The file is already fully retrieved; nothing to do.

---

http_proxy=http://192.168.3.222:8000 wget --server-response --no-cache -c http://ru.archive.ubuntu.com/ubuntu/dists/focal-updates/main/dist-upgrader-all/current/focal.tar.gz
--2020-07-23 19:27:11--  http://ru.archive.ubuntu.com/ubuntu/dists/focal-updates/main/dist-upgrader-all/current/focal.tar.gz
Connecting to 192.168.3.222:8000... connected.
Proxy request sent, awaiting response... 
  HTTP/1.1 416 Requested Range Not Satisfiable
  Server: nginx/1.14.2
  Date: Thu, 23 Jul 2020 16:27:11 GMT
  Content-Type: text/html; charset=utf-8
  Content-Length: 213
  Content-Range: bytes */1336533
  X-Cache: MISS from squid-deb-proxy
  X-Cache-Lookup: HIT from squid-deb-proxy:8000
  Via: 1.1 squid-deb-proxy (squid/3.4.8)
  Connection: keep-alive

    The file is already fully retrieved; nothing to do.

http_proxy=http://192.168.3.222:8000 wget --server-response -c http://ru.archive.ubuntu.com/ubuntu/dists/focal-updates/main/dist-upgrader-all/current/focal.tar.gz
--2020-07-23 19:29:49--  http://ru.archive.ubuntu.com/ubuntu/dists/focal-updates/main/dist-upgrader-all/current/focal.tar.gz
Connecting to 192.168.3.222:8000... connected.
Proxy request sent, awaiting response... 
  HTTP/1.1 200 OK
  Server: nginx/1.14.2
  Date: Thu, 23 Jul 2020 15:15:37 GMT
  Content-Type: application/octet-stream
  Content-Length: 1336533
  Last-Modified: Thu, 16 Jul 2020 08:58:10 GMT
  ETag: "5f1016a2-1464d5"
  Accept-Ranges: bytes
  Age: 4452
  X-Cache: HIT from squid-deb-proxy
  X-Cache-Lookup: HIT from squid-deb-proxy:8000
  Via: 1.1 squid-deb-proxy (squid/3.4.8)
  Connection: keep-alive

    The file is already fully retrieved; nothing to do.

```