pull-ppa-source crashed with ubuntutools.misc.DownloadError in _download_file_from_urls(): Failed to download /tmp/tmpwwavfcfx/openssl_1.0.2g-1ubuntu4.20.dsc

pull-ppa-source crashes when trying to download source packages from a PPA in impish:

e.g.:

$ pull-ppa-source --ppa ubuntu-security-proposed/ppa openssl xenial --no-conf -vvvvvvvvv
pullpkg options: {'login': False, 'verbose': 9, 'download_only': False, 'mirror': None, 'no_conf': True, 'no_verify_signature': False, 'status': [], 'arch': 'amd64', 'pull': 'source', 'distro': 'ppa', 'ppa': 'ubuntu-security-proposed/ppa', 'package': 'openssl', 'release': 'xenial', 'version': None, 'security': False, 'upload_queue': False}
Parsed release 'xenial' pocket 'None'
Distribution: https://api.launchpad.net/devel/ubuntu
DistroSeries: https://api.launchpad.net/devel/ubuntu/xenial
Using distro 'ppa' release 'xenial' pocket 'None'
PersonTeam: https://api.launchpad.net/devel/~ubuntu-security-proposed
Archive: https://api.launchpad.net/devel/~ubuntu-security-proposed/+archive/ubuntu/ppa
Using PPA 'https://launchpad.net/~ubuntu-security-proposed/+archive/ubuntu/ppa'
Calling getPublishedSources(source_name=openssl, exact_match=True, distro_series=https://api.launchpad.net/devel/ubuntu/xenial)
SourcePackagePublishingHistory: https://api.launchpad.net/devel/~ubuntu-security-proposed/+archive/ubuntu/ppa/+sourcepub/12519281
Found openssl 1.0.2g-1ubuntu4.20 in xenial
Parsed <generator object SourcePackage._source_urls at 0x7f40bdb6e430> as /tmp/<generator object SourcePackage._source_urls at 0x7f40bdb6e430>
File not found at <generator object SourcePackage._source_urls at 0x7f40bdb6e430>
Traceback (most recent call last):
  File "/usr/bin/pull-ppa-source", line 12, in <module>
    PullPkg.main(distro='ppa', pull='source')
  File "/usr/lib/python3/dist-packages/ubuntutools/pullpkg.py", line 106, in main
    cls(*args, **kwargs).pull()
  File "/usr/lib/python3/dist-packages/ubuntutools/pullpkg.py", line 426, in pull
    srcpkg.pull()
  File "/usr/lib/python3/dist-packages/ubuntutools/archive.py", line 431, in pull
    Path(self.dsc_pathname).write_bytes(self.dsc.raw_text)
  File "/usr/lib/python3/dist-packages/ubuntutools/archive.py", line 292, in dsc
    self._download_file_from_urls(urls, tmpdsc)
  File "/usr/lib/python3/dist-packages/ubuntutools/archive.py", line 413, in _download_file_from_urls
    raise DownloadError(f'Failed to download {filename}')
ubuntutools.misc.DownloadError: Failed to download /tmp/tmpllz4pb6t/openssl_1.0.2g-1ubuntu4.20.dsc

ProblemType: Crash
DistroRelease: Ubuntu 21.10
Package: ubuntu-dev-tools 0.184
ProcVersionSignature: Ubuntu 5.11.0-25.27-generic 5.11.22
Uname: Linux 5.11.0-25-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu67
Architecture: amd64
CasperMD5CheckResult: unknown
CrashCounter: 1
CurrentDesktop: ubuntu:GNOME
Date: Mon Aug 2 10:38:10 2021
ExecutablePath: /usr/bin/pull-ppa-source
InstallationDate: Installed on 2020-10-11 (294 days ago)
InstallationMedia: Ubuntu 20.10 "Groovy Gorilla" - Beta amd64 (20200930)
InterpreterPath: /usr/bin/python3.9
PackageArchitecture: all
ProcCmdline: /usr/bin/python3 /usr/bin/pull-ppa-source --ppa ubuntu-security-proposed/ppa openssl xenial
Python3Details: /usr/bin/python3.9, Python 3.9.6, python3-minimal, 3.9.4-1
PythonArgs: ['/usr/bin/pull-ppa-source', '--ppa', 'ubuntu-security-proposed/ppa', 'openssl', 'xenial']
PythonDetails: N/A
SourcePackage: ubuntu-dev-tools
Title: pull-ppa-source crashed with ubuntutools.misc.DownloadError in _download_file_from_urls(): Failed to download /tmp/tmpwwavfcfx/openssl_1.0.2g-1ubuntu4.20.dsc
UpgradeStatus: Upgraded to impish on 2021-07-24 (8 days ago)
UserGroups: adm cdrom dialout dip libvirt lpadmin lxd plugdev sambashare sbuild sudo