I noticed this error coming up today, on different rsync mirrors:

~ # eix-sync && emerge -uaNDv world

 * Running emerge --sync
>>> Syncing repository 'gentoo' into '/usr/portage'...
 * Using keys from /usr/share/openpgp-keys/gentoo-release.asc
 * Refreshing keys via WKD .../usr/lib/python3.8/site-packages/urllib3/
connection.py:218: BytesWarning: Comparison between bytes and string
  if SKIP_HEADER not in values:                              [ ok ]
>>> Starting rsync with rsync://46.101.221.22/gentoo-portage/...
>>> Checking server timestamp ...
rsync8.de.gentoo.org

  IPv4:    46.101.221.22
  IPv6:    2a03:b0c0:3:d0::c3:f001 
  Contact: rsync@moonitor.org

The sync'ing completed, on the second attempt.

What is causing the above error?  Can I trust the mirror(s)?