php error unlinking /tmp files

Hi I receive erors in the nginx logs:

‘PHP message: WordPress-Da
2015/05/27 07:26:43 [error] 1490#0: *35698 FastCGI sent in stderr: “PHP message: PHP Fatal error: Uncaught exception ‘RuntimeException’ with message ‘SplFileInfo::getMTime(): stat failed for /var/www/vhosts/mydomain.org/httpdocs/wp-content/tmp/Shariff-e9/Shariff-09b1ec1391b536b215b6e729be920ac5.dat’ in /var/www/vhosts/mydomain.org/httpdocs/wp-content/plugins/shariff-sharing/backend/vendor/zendframework/zend-cache/Zend/Cache/Storage/Adapter/Filesystem.php:154
Stack trace:
#0 /var/www/vhosts/mydomain.org/httpdocs/wp-content/plugins/shariff-sharing/backend/vendor/zendframework/zend-cache/Zend/Cache/Storage/Adapter/Filesystem.php(154): SplFileInfo->getMTime()
#1 /var/www/vhosts/mydomain.org/httpdocs/wp-content/plugins/shariff-sharing/backend/src/Backend.php(41): Zend\Cache\Storage\Adapter\Filesystem->clearExpired()
#2 /var/www/vhosts/mydomain.org/httpdocs/wp-content/plugins/shariff-sharing/backend/index.php(41): Heise\Shariff\Backend->__construct(Array)
#3 /var/www/vhosts/mydomain.org/httpdocs/wp-content/plugins/shariff-sharing/backend/index.php” while reading response header from upstream, client: 147.86.210.7, server: mydomain.org, request: “GET /wp-content/plugins/shariff-sharing/backend/index.php?url=http%3A%2F%2Fwww.mydomain.org%2Fdie-mydomain-zieht-um&temp=%2Fvar%2Fwww%2Fvhosts%2Fmydomain.org%2Fhttpdocs%2Fwp-content%2Ftmp&ttl=60&service=gftlx HTTP/1.1”, upstream: “fastcgi://unix:/var/www/vhosts/system/mydomain.org/php-fpm.sock:”, host: “www.mydomain.org”, referrer: “https://www.mydomain.org/”‘

The /tmp directory is 755 and the shariff-folders and files inside are created absolutely correct.

The plugin seems to work.
Any idea what is going wrong?

Best regards, Christian

https://www.ads-software.com/plugins/shariff-sharing/