SQLSTATE[HY000] [1045] Access denied for user 'root'@'localhost' (using password: YES)

I don’t know where these database parameters are coming from….

I have a EE5 site that I just upgraded from EE2 that works great locally. I’ve deployed the files and db to the development server, and am getting this error: https://d.pr/i/ArJAIp

When I open ee/legacy/database/drivers/mysqli/mysqli_connection.php at line 81, I can see this is an open function for the db connection. If I run die($username) or die($password) on line 76, just above the $this->connection = @new PDO definition, they die with the correct username and password from my database config file. If I hard code the username and password into the $this->connection = @new PDO definition, everything works. However, the connection is erring with root/root as shown in line #0 of the stack trace above. I can see also in that line, that the dbname variable is being recognized, as my db name does start with “au”. This is very confusing… why would it be trying to connect with root/root when the username/password are correctly defined in variables when die()’d in the line above this error?