Thumbnail for pdf generation fails

hi guys,
maybe someone hat this problem before or a solution for it:
i import quite a bunch of PDF-files to the asset-database via console.
the import works perfectly (all mappings to my items done etc) - but thumbnail generation fails…

is it possible to disable thumbnail-generation somehow? or any other hint which imagick-version etc i should use?

18:34:11 ERROR [pimcore] Problem while creating system-thumbnails for image /Produkte/plus.pdf
18:34:11 ERROR [pimcore] ImagickException: unable to open file `/tmp/magick-20871isbrVsbJ7cld’: No such file or directory @ error/constitute.c/ReadImage/544 in /var/www/vendor/pimcore/pimcore/models/Asset/Image.php:227
Stack trace:
#0 /var/www/vendor/pimcore/pimcore/models/Asset/Image.php(227): Imagick->__construct(’/var/www/…’)
#1 /var/www/vendor/pimcore/pimcore/models/Asset/Image.php(88): Pimcore\Model\Asset\Image->generateLowQualityPreview()