You might be experiencing similar issue as Divi theme builder has got on SiteGround.
https://www.siteground.com/kb/divi-builder-timeout-warning/
Please add this code snippet into your .htaccess file:
<ifModule mod_substitute.c> SubstituteMaxLineLength 10M </ifModule>
If it will not help or you need assistance in implementing snippet - submit ticket.
Make sure to share inside support ticket: wp-admin access + FTP details.