False apt_pkg.CacheMismatchError

Python-apt throws CacheMismatchError which is almost certainly false:

Traceback (most recent call last):
  File "/usr/bin/unattended-upgrade", line 2512, in <module>
    sys.exit(main(options))
  File "/usr/bin/unattended-upgrade", line 1986, in main
    res = run(options, rootdir, mem_log, logfile_dpkg,
  File "/usr/bin/unattended-upgrade", line 2398, in run
    new_pending_autoremovals = get_auto_removable(cache)
  File "/usr/bin/unattended-upgrade", line 1789, in get_auto_removable
    return {pkg.name for pkg in cache
  File "/usr/bin/unattended-upgrade", line 1790, in <setcomp>
    if pkg.is_auto_removable}
  File "/usr/lib/python3/dist-packages/apt/package.py", line 1269, in is_auto_removable
    self._pcache._depcache.is_garbage(self._pkg))
apt_pkg.CacheMismatchError: Object of different cache passed as argument to apt_pkg.DepCache method

The relevant code in u-u:

def get_auto_removable(cache):
    # type: (apt.Cache) -> AbstractSet[str]
    return {pkg.name for pkg in cache
            if pkg.is_auto_removable}

---

The Ubuntu Error Tracker has been receiving reports about a problem
regarding unattended-upgrades. This problem was most recently seen with package version 2.1, the problem page at https://errors.ubuntu.com/problem/ff08f6aa104f8e3233da3081835ecc2e9f0452f5 contains more details, including versions of packages affected, stacktrace or traceback, and individual crash reports.
If you do not have access to the Ubuntu Error Tracker and are a software developer, you can request it at http://forms.canonical.com/reports/.