I’m receiving this issue as well, unable to UPDATE the page because of it so pretty critical error.

No files are corrupt did a clean install of the theme twice.

PHP 7.1, Ubuntu 16.04.2, Apache/2.4.18, Enfold 4.0.5, WordPress 4.7.4

Happens after editing a slide / creating a new slide, hit page UPDATE, get white screen, no changes save. Server log gets:

[php7:warn] PHP Warning: A non-numeric value encountered in /wordpress/wp-content/themes/enfold/config-templatebuilder/avia-template-builder/php/html-helper.class.php on line 1054, referer: …/wp-admin/post.php?post=504&action=edit