A Wordpress site with woocommerce runs with php mode Fast-CGI (but makes fcgid:warn]. However, changed to php mode PHP-FPM it stops working completely, only white screen and nothing happens and nothing in logs. Any idea why PHP-FPM does not work? Usually I have found PHP-FPM is least problematic PHP mode.
Check website error.log. Most likely there is a PHP module missing that the site is using which is available in FastCGI php.
Also check if you have php-fpm running in chroot mode, as all file paths would need adjusted if switching between chroot (php-fpm) and non-chroot (fastcgi) modes.