我的网络中有一个 apt 缓存服务器，我应该连接到它，我已经配置了代理设置，但是当我尝试连接时出现此错误：
Err:1 https://download.docker.com/linux/ubuntu bionic InRelease
Invalid response from proxy: HTTP/1.1 403 SSL CONNECT proxying not configured Connection: close Date: Wed, 18 Mar 2020 09:11:14 GMT Server: apt-cacher/1.7.11 Content-Length: 0 [IP: 10.x.x.x 3142]
Err:2 http://us.archive.ubuntu.com/ubuntu bionic InRelease
Connection failed [IP: x.x.x.x 3142]
Err:3 http://us.archive.ubuntu.com/ubuntu bionic-security InRelease
Connection failed [IP: 10.x.x.x 3142]
Err:4 http://us.archive.ubuntu.com/ubuntu bionic-updates InRelease
Connection failed [IP: 10.x.x.x 3142]
Err:5 http://us.archive.ubuntu.com/ubuntu bionic-proposed InRelease
Connection failed [IP: x.x.x.x 3142]
Err:6 http://us.archive.ubuntu.com/ubuntu bionic-backports InRelease
Connection failed [IP: x.x.x.x 3142]
Reading package lists... Done
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/bionic/InRelease Connection failed [IP: 10.x.x.x 3142]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/bionic-security/InRelease Connection failed [IP: 10.x.x.x 3142]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/bionic-updates/InRelease Connection failed [IP: 10.x.x.x 3142]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/bionic-proposed/InRelease Connection failed [IP: 10.x.x.x 3142]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/bionic-backports/InRelease Connection failed [IP: 10.x.x.x 3142]
W: Failed to fetch https://download.docker.com/linux/ubuntu/dists/bionic/InRelease Invalid response from proxy: HTTP/1.1 403 SSL CONNECT proxying not configured Connection: close Date: Wed, 18 Mar 2020 09:11:14 GMT Server: apt-cacher/1.7.11 Content-Length: 0 [IP: 10.x.x.x 3142]
W: Some index files failed to download. They have been ignored, or old ones used instead.
正如您在第一行看到的那样，似乎我可以连接到缓存器 repo 服务器，但是为什么会发生这个错误？