Galera Node missing binlog entries from other nodes dispite log_slave_updates=ON

I am using one node of a 3-node-Clusters as Master for a slave. On all node log_slave_updates is set to ON. Still we occasionaly encounter missing records when processing updates from the binary logs on the slave. Analyzing the binary logs on the cluster nodes I found that most of the changes applied on other nodes are reflected on the node serving as master but some are not. And it is unpredectable when this happens.

This problem is a real blocker because the result is that the replication breaks whenever such a problem occurs and the binary logs are not usable for point in time recovery.