From the systemd release notes:
nss-mymachines lost support for resolution of users and groups, and now
only does resolution of hostnames. This functionality is now provided by
nss-systemd. Thus, the 'mymachines' entry should be removed from the
'passwd:' and 'group:' lines in /etc/nsswitch.conf (and 'systemd' added
if it is not already there).