recurring PHP warning

I’m experiencing a recurring PHP warning on my WordPress site related to the Cache Enabler plugin. The issue appears even after clearing the cache and reoccurs once the cache is rebuilt.

Warning: preg_match(): Unknown modifier ‘p’ in /home/httpd/vhosts/sergesellsretro.ch/shop.sergesellsretro.ch/wp-content/plugins/cache-enabler/inc/cache_enabler_engine.class.php on line 352
Warning: Cannot modify header information – headers already sent by (output started at /home/httpd/vhosts/sergesellsretro.ch/shop.sergesellsretro.ch/wp-content/plugins/cache-enabler/inc/cache_enabler_engine.class.php:352) in /home/httpd/vhosts/sergesellsretro.ch/shop.sergesellsretro.ch/wp-content/plugins/wpvivid-imgoptim/includes/cdn/class-wpvivid-cdn.php on line 50
Warning: Cannot modify header information – headers already sent by (output started at /home/httpd/vhosts/sergesellsretro.ch/shop.sergesellsretro.ch/wp-content/plugins/cache-enabler/inc/cache_enabler_engine.class.php:352) in /home/httpd/vhosts/sergesellsretro.ch/shop.sergesellsretro.ch/wp-content/plugins/wpvivid-imgoptim/includes/cdn/class-wpvivid-cdn.php on line 55
Warning: Cannot modify header information – headers already sent by (output started at /home/httpd/vhosts/sergesellsretro.ch/shop.sergesellsretro.ch/wp-content/plugins/cache-enabler/inc/cache_enabler_engine.class.php:352) in /home/httpd/vhosts/sergesellsretro.ch/shop.sergesellsretro.ch/wp-content/plugins/wpvivid-imgoptim/includes/cdn/class-wpvivid-cdn.php on line 56

The issue seems to originate from the following line inside Cache Enabler:
preg_match(‘/^https?://’ . $_SERVER[‘HTTP_HOST’] . ‘/’, $url);

Thank you very much for your help!