Error on frontend

sometimes our website displays an error message on the frontend:
Warning: opendir(/var/www/[site]/wp-content/plugins/var/www/[otherSite]/wp-content/plugins/seo-ultimate/modules): failed to open dir: No such file or directory in /var/www/[site]/wp-content/plugins/seo-ultimate/plugin/class.seo-ultimate.php on line 462
Warning: readdir() expects parameter 1 to be resource, boolean given in /var/www/[site]/wp-content/plugins/seo-ultimate/plugin/class.seo-ultimate.php on line 465

The [otherSite] revers to one of the other wordtpress sites running from the same server

https://ww.wp.xz.cn/plugins/seo-ultimate/