Maxscale sometimes (not always!) doesn't authenticate user via Splitter servise

Maxscale works but SOME queries fail with authentification error (it can happen for any user):

*020-03-03 13:30:01 error : [MySQLAuth] Client hostname lookup failed, getnameinfo() returned: 'Name or service not known'.
2020-03-03 13:30:01 warning: [MySQLAuth] Splitter Service: login attempt for user 'testfromast1'@[172.20.71.193]:54860, authentication failed.
2020-03-03 13:30:01 notice : [MySQLAuth] [Splitter Service] Loaded 127 MySQL users for listener Splitter Listener.
2020-03-03 13:30:01 error : [MySQLAuth] Client hostname lookup failed, getnameinfo() returned: 'Name or service not known'.
2020-03-03 13:30:01 warning: [MySQLAuth] Splitter Service: login attempt for user 'call_states'@[172.20.71.109]:55948, authentication failed.
2020-03-03 13:33:02 error : [MySQLAuth] Client hostname lookup failed, getnameinfo() returned: 'Name or service not known'.
2020-03-03 13:33:02 notice : [MySQLAuth] [Splitter Service] Loaded 127 MySQL users for listener Splitter Listener.
2020-03-03 13:33:02 notice : [MySQLAuth] [Splitter Service] Loaded 127 MySQL users for listener Splitter Listener.
2020-03-03 13:33:02 error : [MySQLAuth] Client hostname lookup failed, getnameinfo() returned: 'Name or service not known'.
2020-03-03 13:33:02 warning: [MySQLAuth] Splitter Service: login attempt for user 'call_states'@[172.20.71.109]:55976, authentication failed.*

These users exist with wildcard like 'user'@'%', most of queries done well.

Here are my maxscale permissions on backend servers:

GRANT SHOW DATABASES, REPLICATION SLAVE, REPLICATION CLIENT ON *. TO 'maxscale'@'172.31.254.61' |

Here is my /etc/maxscale.cnf:

*[maxscale]
threads=4
auth_connect_timeout=20
auth_read_timeout=20
auth_write_timeout=20
log_warning=1
log_info=0

[Splitter Service]
type=service
router=readwritesplit
router_options=master_accept_reads=true
servers=node1, node2
user=maxscale
passwd=PASSWD

[Splitter Listener]
type=listener
service=Splitter Service
protocol=MySQLClient
port=3306
address=0.0.0.0
socket=/tmp/ClusterMaster

[node1]
type=server
address=172.31.254.55
port=3306
protocol=MySQLBackend
priority=1

[node2]
type=server
address=10.77.12.33
port=3306
protocol=MySQLBackend
priority=2

[Galera Monitor]
use_priority=true
disable_master_failback=true
type=monitor
module=galeramon
servers=node1, node2
user=maxscale
passwd=PASSWD

[CLI]
type=service
router=cli

[CLI Listener]
type=listener
service=CLI
protocol=maxscaled
port=6603*