mysql version is 5.5 and it has no option for GTIDs, so

gtid_mode                 = on
enforce_gtid_consistency  = on

cannot be set. The MySQL connector documentation already states this is optional, but at line 191 of io.debezium.connector.mysql.SnapshotReader.java the following line requires a 5th column in the SHOW MASTER STATUS result set:

String gtidSet = rs.getString(5)

Since earlier versions of MySQL do not have a 5th column, this results in an index out of range and it register success. However, it won't create the Kafka topic or change event stream.