Using too big key for internal temp tables

Hi,

We have got many error when we restart our maxscale services

2019-01-08 20:36:59 error : [MySQLAuth] Failed to load users from server 'xx.xx.xx.xx': Internal error: Using too big key for internal temp tables

2019-01-08 20:36:59 notice : [MySQLAuth] [RWSVC] No users were loaded but 'inject_service_user' is enabled. Enabling service credentials for authentication until database users have been successfully loaded.

It begin with 10 or 15 warning per day, and for last few days we can't log into the database through maxscale.

Maxscale is able to telnet database server on port 3306, with maxscale account it can log in and show user database.

Direct access to database is okay with same account.

Not a network or a firewall problem.

Maxscale version 2.2.18
DB version : MariaDB 10.3.2

Could you help us ?

Thx