unsupported authenticator plugin

after upgrading to maxscale 2.5 we see the following hapening:

2020-07-26 13:44:34 info : (112318) [MariaDBAuth] Client 'centralqueue'@'138.203.58.136' is using an unsupported authenticator plugin ''. Trying to switch to 'mysql_native_password'.

but if we check the server we see the following:
MariaDB [(none)]> SELECT User, Host, Plugin from mysql.user where User = 'centralqueue';
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1 row in set (0.001 sec)

so its set to mysql native, but maxscale does not see this.
it seems this only happens for older clients