After further testing, this is untrue. define(‘WP_MEMORY_LIMIT’, ‘500M’); overrides the default constant of 32M (multisite) or 64M (single site). You also have to override the define( ‘WP_MAX_MEMORY_LIMIT’, ‘256M’ ); by adding a second define to the wp-config.php file of define( ‘WP_MAX_MEMORY_LIMIT’, ‘500M’ );
That solves the problem. You can mark this as resolved.
Just so everyone knows, txantimedia‘s solution above worked for me! So grateful to have found this.
Thanks!