session closed by maxscale when it received "auth switch request" packet from backend server

maxscale.cnf like this:
[maxscale]
threads=auto
...
[server1]
type=server
address=10.197.0.230
port=3306
protocol=MariaDBBackend
[server2]
type=server
address=10.197.0.110
port=3307
protocol=MariaDBBackend
[server3]
type=server
address=10.197.0.33
port=3307
protocol=MariaDBBackend

[MariaDB-Monitor]
type=monitor
module=mariadbmon
servers=server1,server2,server3
user=maxscale
password=xxx
monitor_interval=10000

[Splitter-Service]
type=service
router=readwritesplit
servers=server1,server2,server3
user=maxscale
password=xxx
enable_root_user=1

[Splitter-Listener]
type=listener
service=Splitter-Service
protocol=MariaDBClient
port=4006

When use "mysql -ubackmanager -pxxx -hmaxscale-host -P4006" from one mysql slave node like server2, it is OK to enter mysql command line. But return "ERROR 1927 (08S01): Connection killed by MaxScale: Router could not recover from connection errors" when input any sql statement.
I tried to catch packet between maxscale and server, and fund maxscale get "auth switch request" packet from server, then maxscale send fin packet to server to finish this session. The packet I got is attached.