As per https://metacpan.org/pod/LWP::UserAgent#request,

  Note that errors writing to the content file (for example due to permission
  denied or the filesystem being full) will be reported via the Client-Aborted
  or X-Died response headers, and not the is_success method.

We were already handling X-Died specially, but not Client-Aborted,
so there could be cases when we later treated the download as failed
(due to size or hash mismatch) but did not report about the origin
of the problem, which would make debugging of user bug reports harder.