Linux Mint 18 Erro de atualização do apt-get: Falha na conexão em algumas fontes

Question

Quando executo '' sudo-apt-get update ', alguns arquivos não podem ser baixados:

E: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial/main/binary-amd64/Packages  Connection failed [IP: 91.189.88.161 80]
E: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-updates/main/binary-amd64/Packages  Connection failed [IP: 91.189.88.161 80]
E: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/xenial-backports/main/binary-amd64/Packages  Connection failed [IP: 91.189.88.161 80]

Mais mensagens de erro:

W: The repository 'http://archive.ubuntu.com/ubuntu xenial Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: The repository 'http://archive.ubuntu.com/ubuntu xenial-updates Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: The repository 'http://archive.ubuntu.com/ubuntu xenial-backports Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.

O que eu fiz:

sudo apt-get clean
sudo rm -rf /var/lib/apt/lists/*

Mas o problema ainda persiste.

Aqui está o que está no meu diretório sources.list.d/ , caso ele forneça informações úteis:

maarten-baert-simplescreenrecorder-xenial.list
neovim-ppa-stable-xenial.list
nodesource.list
official-package-repositories.list
vscode.list
yarn.list

Como posso consertar isso? Este é o meu primeiro erro de apt-get no linux mint 18, e o Google não fornece nenhum resultado útil.