I had the same problem and just fixed it. The problem happened when I moved the site from newsite.example.com to example.com. I forgot about the custom work done on the wp-config.php file before I moved the site. The custom work was meant to source the “my-content” directory instead of “wp-content”.
On the wp-config.php file I changed:
define( 'WP_CONTENT_URL', 'https://newsite.example.com/my-content');
to:
define( 'WP_CONTENT_URL', 'https://example.com/my-content');
I hope this helps.
