binlog_encryption.rpl_gtid_basic failed in buildbot, couldn't start mysqld.4

binlog_encryption.rpl_gtid_basic 'innodb,ncmpr,stmt' w2 [ fail ]

        Test ended at 2018-08-03 13:38:43

CURRENT_TEST: binlog_encryption.rpl_gtid_basic

Failed to start mysqld.4

mysqltest failed but provided no output

The result from queries just before the failure was:

< snip >

INSERT INTO t1 VALUES (34);

connection server_2;

connection server_3;

include/start_slave.inc

SELECT * FROM t1 WHERE a >= 30 ORDER BY a;

a

31

32

33

34

connection server_4;

SELECT * FROM t1 WHERE a >= 30 ORDER BY a;

a

31

32

33

34

connection server_1;

DROP TABLE t1;

include/rpl_end.inc