[Smartcrawl] I cannot edit main page in dashboard

During the chat we follow those threads to fix the issue on my side
https://premium.wpmudev.org/forums/topic/smartcrawl-deactivate-postpage-editor
https://premium.wpmudev.org/forums/topic/smartcrawl-throws-a-500-error-when-saving-a-post-as-draft
but that does not help.
I contact with host, they enabled "mb_string" and restarted the server, but issue still exist.

I see this in debug.log
PHP Fatal error: Call to undefined function mb_detect_encoding() in /home/++/public_html/wp-content/plugins/wpmu-dev-seo/includes/external/simple_html_dom.php on line 1234