When I execute this Statements:
CREATE DATABASE IF NOT EXISTS ReplicationBug;
CREATE TABLE IF NOT EXISTS ReplicationBug.Test (id int(10));
CREATE OR REPLACE TRIGGER ReplicationBug.NotReplicatingTrigger
BEFORE INSERT
ON ReplicationBug.Test
FOR EACH ROW
BEGIN
SET NEW.id = 100;
END;

And than (I change the Value which i assign to the NEW.id to 200):
CREATE OR REPLACE TRIGGER ReplicationBug.NotReplicatingTrigger
BEFORE INSERT
ON ReplicationBug.Test
FOR EACH ROW
BEGIN
SET NEW.id = 200;
END;

The change to the trigger is only on one node of the galera cluster. The other nodes still have the old trigger definition, which assignes NEW.id the value of 100.

Looking in the mysqld.log of one of the nodes which did not replicate, I get the following error message:
2020-01-27 14:43:54 13 [ERROR] Slave SQL: Error 'Trigger 'ReplicationBug.NotReplicatingTrigger' already exists' on query.
It seems that "CREATE OR REPLACE TRIGGER" is transformed to "CREATE TRIGGER" on the other nodes.

TL/TD:
The replication of "CREATE OR REPLACE TRIGGER" statements is not working on our galera cluster.