I have struck this twice in two successive Wordpress installations on two different brand new servers.
The WordPress script is not copying the entire automatically generated password from the script installer to wp-config.php.
Here is an example showing what CWP put in and, the password its meant to be is shown below it.
/** MySQL database password */
define( 'DB_PASSWORD', '?-lWdWw*' );
This is what the password is supposed to be ?-lWdWw*$D00
As i said, two brand new servers, with fresh installations...and twice in a row the Wordpress Automated installer script has thrown a "cannot connect to database" error because the wp-config.php file mysql password as entered into wp-config.php by CWP is incomplete!
I must reinforce...this is the automatically generated password done by CWP itself (not a manual password i entered).
I wonder if it may have something to do with the screen size and resolution on the laptop device i used to do this. On both occasions, the password box wasn't wide enough to display the full automatically generated password (not sure if this has anything to do with developers problem solving this one...but i thought i would add that just in case). There is definitely a bug here.