ClassLoader.php?!

Hi Support,

We have hundreds errors in our error log. We always see this:
” failed to open stream: Too many open files in mydomain.com/public_html/wp-content/plugins/better-wp-security/vendor-prod/composer/ClassLoader.php on line 444, referer https://mydomain.com/wp-admin/ ”

What is causing this? And how could we fix it?
We are running on the last update.

Thanks!