Julian, thanks for your patience. I'm not able to offer a shell on the affected machine, so debugging this is just going to have to go at a snail's pace.
I read strace and ltrace logs from both 1.2.12-ish and 1.2.15 apt packages and narrowed it down to /usr/bin/apt-key.
When I use the /usr/bin/apt-key from apt_1.2.12~ubuntu16.04.1_amd64.deb (but everything else from 1.2.15 packaging) my apt-get update runs as I expect.
Julian, thanks for your patience. I'm not able to offer a shell on the affected machine, so debugging this is just going to have to go at a snail's pace.
I read strace and ltrace logs from both 1.2.12-ish and 1.2.15 apt packages and narrowed it down to /usr/bin/apt-key.
When I use the /usr/bin/apt-key from apt_1.2. 12~ubuntu16. 04.1_amd64. deb (but everything else from 1.2.15 packaging) my apt-get update runs as I expect.
I'll attach the diff between the two (NOT A FIX).
Thanks