Setting wsrep_slave_threads causes thread hang

SET GLOBAL wsrep_cluster_address=AUTO;

SET GLOBAL wsrep_slave_threads=12;

11.0.1-opt>SHOW PROCESSLIST;

+----+------+-----------+------+---------+------+----------+-----------------------------------+----------+

| Id | User | Host      | db   | Command | Time | State    | Info                              | Progress |

+----+------+-----------+------+---------+------+----------+-----------------------------------+----------+

|  4 | root | localhost | test | Query   | 7972 | NULL     | SET GLOBAL wsrep_slave_threads=12 |    0.000 |

|  5 | root | localhost | test | Query   |    0 | starting | SHOW PROCESSLIST                  |    0.000 |

+----+------+-----------+------+---------+------+----------+-----------------------------------+----------+

2 rows in set (0.000 sec)