wp-config issue

Just a suggestion.

For security I have placed wp-config one directory below the WP installation(root)

When I changed the prefix it said that the wp-config had been altered, but it wasn’t.
I altered this manually, but you may want to look into this scenario as WP security is ramping up and there will be more installation like this
(All mine are!)

https://ww.wp.xz.cn/plugins/db-prefix-change/