php fastcgi is not working = 500 (fpm works)

Hi,

If I switch from php-fpm(7.2.14) to php-fastCGi i get ERROR 500.

The Log shows me mod_fcgid: stderr: PHP Fatal error: Uncaught RuntimeException: Unable to write in the Proxy directory (/var/www/vhosts/domain.com/httpdocs/var/cache/production_201812/proxies)

First I thought it's a permission thing, but fpm works and vhost root is usr psasrv, Folder&Files are usr psacln

Has anyone a hint for me?

Tahnks you

Debian9.7 Plesk17.8.11 Update #37 PHP7.2.14 (Same modules active)