main.flush_read_lock failed in buildbot with XAER_NOTA: Unknown XID

main.flush_read_lock 'innodb'            w4 [ fail ]

        Test ended at 2020-06-19 08:30:54

CURRENT_TEST: main.flush_read_lock

mysqltest: At line 1724: query 'reap' failed: 1397: XAER_NOTA: Unknown XID

The result from queries just before the failure was:

< snip >

# Switching to connection 'default'.

connection default;

# Send XA ROLLBACK 'test1'

xa rollback 'test1';

# Switching to connection 'con1'.

connection con1;

# Wait until XA ROLLBACK is blocked.

Timeout in wait_condition.inc for select count(*) = 1 from information_schema.processlist

where state = "Waiting for backup lock" and

info = "xa rollback 'test1'"

Id	User	Host	db	Command	Time	State	Info	Progress

268	root	localhost	test	Sleep	30		NULL	0.000

269	root	localhost	test	Query	0	starting	show full processlist	0.000

270	root	localhost	test	Sleep	30		NULL	0.000

271	root	localhost	test	Sleep	33		NULL	0.000

unlock tables;

flush tables with read lock;

# Switching to connection 'default'.

connection default;

# Reap XA ROLLBACK