Old wp-config is valid.

There seem to be an issue with parsing your old wp-config file. A new one will be created.

The installer can only modify a standard wp-config.php that contains the database access constants and is correctly formed. It cannot modify custom wp-config.php that, for example, includes other files in which database connection information is written. In this case, the installation can continue normally by generating a new wp-config.php from wp-config-sample.php, and the original wp-config.php will be lost.

• Check if you have not made any adjustments to your wp-config and removed the database constants.
• Check with your hosting provider if they handle the wp-config differently form the standard WordPress wp-config.