I ran into this same issue. I ended up running a text search in ssh to find “memory_limit” and it said there was a reference in /wp-includes/default-constants.php and changed:
define( 'WP_MAX_MEMORY_LIMIT', '256M' );
to
define( 'WP_MAX_MEMORY_LIMIT', '7000M' );
(set this to a lower number based on your available ram)
and that did the trick for me.
