Failure to create source archives while updating timestamps

ERROR:workitem.py:944(14098): Unable to create source archives for workitem qt/qtdeclarative/8ce51e03cd8728bf5da668dc9fcbc38e9e1d6354/MacOSMacOS_10_14x86_64IOSIOS_ANYarm64Clangqtci-macos-10.14-x86_64-62e428/8cf4fea662501a2cf6aead23ed771940252e60af/Test:   RAN: tar cf /home/vmbuilder/ci-working-dir/storage/qt/qtdeclarative/fef8a8cfee50d6dedb9f68fc4a88ac7cfad99674/sources_unix_partial -C /tmp/coin-src-archive-e7pcrtpufef8a8 . --mtime=Wed, 15 Apr 2020 07:09:14 +0200  STDOUT:
  STDERR:
tar: /home/vmbuilder/ci-working-dir/storage/qt/qtdeclarative/fef8a8cfee50d6dedb9f68fc4a88ac7cfad99674/sources_unix_partial: Wrote only 2048 of 10240 bytes
tar: Error is not recoverable: exiting nowTraceback (most recent call last):
  File "/home/vmbuilder/qt-ci/src/workitem.py", line 934, in _createSourceArchive
    await asyncio.wait_for(createArchiveCoro, timeout=self.waitingForSourceArchiveCreatedTimeout, loop=self.loop)
  File "/usr/local/share/python3.8.0/lib/python3.8/asyncio/tasks.py", line 483, in wait_for
    return fut.result()
  File "/home/vmbuilder/qt-ci/src/storage.py", line 432, in createSourceArchives
    await asyncio.gather(*(storage.ensureSourceArchive(*args) for args in toExecute), loop=loop)
  File "/home/vmbuilder/qt-ci/src/storage.py", line 358, in ensureSourceArchive
    await asyncio.gather(*(self._archive(
  File "/home/vmbuilder/qt-ci/src/storage.py", line 346, in _archive
    await archiveCoro
  File "/home/vmbuilder/qt-ci/src/repositorymanager.py", line 411, in archive
    await ash.tar("cf", targetArchive, "-C", tmpdir.name, ".", f"--mtime={authorDate.splitlines()[0]}")
  File "/home/vmbuilder/qt-ci/src/ash.py", line 145, in __call__
    raise sh.ErrorReturnCode_128(" ".join(processed_args), stdout, stderr)
sh.ErrorReturnCode_128:   RAN: tar cf /home/vmbuilder/ci-working-dir/storage/qt/qtdeclarative/fef8a8cfee50d6dedb9f68fc4a88ac7cfad99674/sources_unix_partial -C /tmp/coin-src-archive-e7pcrtpufef8a8 . --mtime=Wed, 15 Apr 2020 07:09:14 +0200  STDOUT:
  STDERR:
tar: /home/vmbuilder/ci-working-dir/storage/qt/qtdeclarative/fef8a8cfee50d6dedb9f68fc4a88ac7cfad99674/sources_unix_partial: Wrote only 2048 of 10240 bytes
tar: Error is not recoverable: exiting now