this may(!) indicate an issue with the database. Try to repair the database using the following instructions: https://www.ads-software.com/support/article/editing-wp-config-php/#automatic-database-optimizing

While editing wp-config.php, you may also want to set values for the site URL (https://www.ads-software.com/support/article/editing-wp-config-php/#wp_siteurl) and blog address URL (https://www.ads-software.com/support/article/editing-wp-config-php/#blog-address-url)

If all that fails, make sure that your database is fully converted, and that the old url is replaced with the new url. This includes instances of the url in serialized data. If you can use plugins, check out: https://www.ads-software.com/plugins/search-and-replace/

If you don’t have access to the wp-dashboard, check this out: https://interconnectit.com/products/search-and-replace-for-wordpress-databases/

Once (hopefully) all is working fine, remove the code that you’ve added to the wp-config.php file.