I had included /etc/firewalld in the configuration, and when syncing via csync -xv, the remote node logged Updated /etc/firewalld/services/cluster.xml from XXX.
But in fact on that host the directory /etc/firewalld/services was missing, so there was no cluster.xml after sync.
Only after I had created the directory manually, csync was actually successful.
There should not be a mis-leading syslog message.
Version being used was from SLES15 SP2 (csync2-2.0+git.1461714863a4-4.3.1.x86_64).