Comment 8 for bug 1795207

I resolved this problem by modifying my /etc/apt/sources.list to remove the mirror method, and point directly to ubuntu sources. I.e. my old sources.list contained lines like this:

  deb mirror://mirrors.ubuntu.com/mirrors.txt xenial main restricted

Which I modified to this:

  deb http://us.archive.ubuntu.com/ubuntu/ xenial main restricted