dh key too small on one WP instance but not on the other (identical)

I have two WP websites, updated at WP 4.9.6 running on same server with php7-fpm and nginx, connecting to same mysql server 5.6.10.
Same config:

define( 'MYSQL_CLIENT_FLAGS', MYSQLI_CLIENT_SSL | MYSQLI_CLIENT_SSL_DONT_VERIFY_SERVER_CERT );
define( 'MYSQL_SSL_CIPHER', 'HIGH:!aNULL:!MD5:!RC4:!DHE');
//define( 'MYSQL_SSL_CIPHER', 'AES256-SHA:AES256-RMD:DES-CBC3-RMD:RC4-SHA:DES-CBC3-SHA:DES-CBC-SHA:EDH-RSA-DES-CBC3-SHA:EDH-RSA-DES-CBC-SHA');

One works like a charm the other gave me this error:

PHP Warning:  mysqli_real_connect(): SSL operation failed with code 1. OpenSSL Error messages:
error:141A318A:SSL routines:tls_process_ske_dhe:dh key too small in /wp-includes/wp-db.php on line 1531

Seems it’s not considering the MYSQL_SSL_CIPHER param. Is there anything else I could do to troubleshoot this problem.