Slave configured with GTID crashed because of :

2019-11-11 21:29:23 9291 [ERROR] Slave SQL: Could not execute Update_rows_v1 event on table magazine.user_master; Duplicate entry '711407' for key 'PRIMARY', Error_code: 1062; handler error HA_ERR_FOUND_DUPP_KEY; the event's master log mysql-bin.065811, end_log_pos 441166884, Gtid 0-122-179115583, Internal MariaDB error code: 1062
2019-11-11 21:29:23 9291 [Warning] Slave: Duplicate entry '711407' for key 'PRIMARY' Error_code: 1062
2019-11-11 21:29:23 9291 [ERROR] Error running query, slave SQL thread aborted. Fix the problem, and restart the slave SQL thread with "SLAVE START". We stopped at log 'mysql-bin.065811' position 441165623; GTID position '0-122-179115582'
2019-11-11 21:29:23 9291 [Note] Slave SQL thread exiting, replication stopped in log 'mysql-bin.065811' at position 441165623; GTID position '0-122-179115582'

The slave is read only, with 2 accounts root and user for replication. Binlog format is row for master and log.
After checking master binary log i found this:

UPDATE `user_master` SET `delivery_method` = 3 WHERE `num` = 711407 GTID 0-122-179115579
UPDATE `user_master` SET `delivery_method` = 10 WHERE `num` = 711407 GTID 0-122-179115580
UPDATE `user_master` SET `delivery_method` = 3 WHERE `num` = 711407 GTID 0-122-179115581
UPDATE `user_master` SET `delivery_method` = 10 WHERE `num` = 711407 GTID 0-122-179115582
UPDATE `user_master` SET `delivery_method` = 3 WHERE `num` = 711407 GTID 0-122-179115583

Where to start investigating this ? At what to look for this situations ?