`galera_3nodes.galera_ipv6_mariabackup` fails

galera_3nodes.galera_ipv6_mariabackup 'innodb' w3 [ fail ]
Test ended at 2020-02-19 07:08:33

CURRENT_TEST: galera_3nodes.galera_ipv6_mariabackup
mysqltest: In included file "./include/assert_grep.inc":
included from /home/timofey_turenko_mariadb_com/mtr-galera-test/MariaDBEnterprise/mysql-test/suite/galera_3nodes/t/galera_ipv6_mariabackup.test at line 70:
At line 152: assert_grep.inc failed.

The result from queries just before the failure was:
< snip >
INSERT INTO t1 VALUES (1);
connection node_2;
SET GLOBAL wsrep_provider_options='gmcast.isolate=0';
SELECT COUNT = 1 FROM t1;
COUNT = 1
1
DROP TABLE t1;
connection node_1;
include/assert_grep.inc [Streaming the backup to joiner at [::1]]
include/assert_grep.inc [async IST sender starting to serve tcp://[::1]:]
include/assert_grep.inc [IST receiver addr using tcp://[::1]]
include/assert_grep.inc [Prepared IST receiver for 3-6, listening at: tcp://[::1]]
include/assert_grep.inc failed!
assert_text: 'Prepared IST receiver for 3-6, listening at: tcp://[::1]'
assert_file: '/var/tmp/mtr/3/log/mysqld.2.err'
assert_select: 'Prepared IST receiver for 3-6, listening at: tcp://[::1]'
assert_match: ''
assert_count: '1'
assert_only_after: 'CURRENT_TEST'
number of matching lines: 0

More results from queries before failure can be found in /var/tmp/mtr/3/log/galera_ipv6_mariabackup.log

• skipping '/var/tmp/mtr/3/log/galera_3nodes.galera_ipv6_mariabackup-innodb/'

Retrying test galera_3nodes.galera_ipv6_mariabackup, attempt(2/3)...