I did a routine Ubuntu system update for security patches today (2018-02-21)... mssql will no longer start or update, seeing failures in error log, systemctl and update output with 404 like:
Err:13 https://packages.microsoft.com/ubuntu/16.04/mssql-server xenial/main amd64 Packages
404 Not Found
Problem: routine update breaks my vanilla Ubuntu 16 LTS with mssql-server instance. No other substantive info obvious to me looking in logs, etc...