Hello,
Please provide us with wp-admin access to the site with the speed problem so we could check the problem deeply.
Also, make sure that all required plugins are updated https://www.8theme.com/download-plugins/ (to update free plugins just click on update link from your Dashboard (Plugins > Installed Plugins); to update premium plugins, connect to your server using FTP. Copy extracted plugins folders into wp-content/plugins/ )
Regards