After configuring a test environment using Multi-DB I am able to create sub sites and the databases appear to create but when I click on view site I get an error .
"Error establishing a database connection "
When viewing the site details via the dashboard - wp-admin/network/site-info.php?id=18 I see the following notice
Notice: Undefined index: scheme in /var/www/wp-admin/network/site-info.php on line 129
Does this mean anything to you?