I can confirm this. After upgrade to 2.6.6 version got broken site and these PHP errors:
PHP Fatal error: require_once(): Failed opening required 'vendor/autoload.php' (include_path='.:/opt/alt/php74/usr/share/pear') in /home/itzdcqhx/public_html/wp-content/plugins/woo-payment-gateway-paysera/paysera.php on line 26
PHP Warning: require_once(vendor/autoload.php): failed to open stream: No such file or directory in /home/itzdcqhx/public_html/wp-content/plugins/woo-payment-gateway-paysera/paysera.php on line 26
Rolled back to 2.6.4 by now. Please fix this.