unattended-upgrades uses between 60 and 100% of one CPU until service restarted

today I caught unattended-upgrades doing pretty much nothing but using up most of one CPU on three hosts: submit-01, mx-dal-01 and srs-dal-01.

From what I could see, the process is trying to open a couple of files that don't exist, followed by sending some data on a file descriptor which is a socket towards I don't know what and then polling that socket a couple of times, and finally looping to do exactly the same thing again.

I found issues that seem somewhat related but they don't have the detail about polling a socket, so I'm not certain that we're hitting exactly the same thing:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1012752

the issue goes away when I restart the unattended-upgrades service