WP-SMUSH-PRO causes error 500

Since yesterday wp-smush-pro update, I get error 500 on every page of the site. I had to disable the plugin.
Here is what I get in the log files:

PHP message: PHP Fatal error:  Allowed memory size of 402653184 bytes exhausted (tried to allocate 81 bytes) in /var/www/web1/wp-includes/wp-db.php on line 1832

please note that the actual file where I get the error changes every time. What can I do to make it work again?