Hey 🙂
I face the same issue since the update to 4.9 version – error log is polluted with those errors.
2019/01/08 19:53:58 [error] 12495#12495: *569870 FastCGI sent in stderr: “PHP message: PHP Warning: file_put_contents(/www/apollo13****/public/wp-content/uploads/wpdm-cache//session-e7fd34941370f62ca683a34f82111f82.txt): failed to open stream: No such file or directory in /www/apollo13****/public/wp-content/plugins/download-manager/libs/class.Session.php on line 75” while reading response header from upstream, client: ****
After deactivation -> activation of plugin only “wpdm-file-type-icons” directory was created but still not “wpdm-cache”.
Please also note double slash in “uploads/wpdm-cache//”.
With kind regards.