Fatal Error Trying to Edit Page

Hello,

When trying to edit the homepage of the site, an error shows up:
The site is experiencing technical difficulties. Please check your site admin email inbox for instructions.

The email states:

“Howdy!

Since WordPress 5.2 there is a built-in feature that detects when a plugin or theme causes a fatal error on your site, and notifies you with this automated email.

In this case, WordPress caught an error with your theme, Enfold.”

The email list the following error details:

Error Details
=============
An error of type E_ERROR was caused in line 1199 of the file /www/wp-content/themes/enfold/config-templatebuilder/avia-template-builder/php/shortcode-template.class.php. Error message: Uncaught TypeError: Argument 1 passed to aviaShortcodeTemplate::set_frontend_developer_heading_tag() must be of the type array, string given, called in /www/wp-content/themes/enfold/config-templatebuilder/avia-shortcodes/av-helper-slideshow.php on line 354 and defined in /www/wp-content/themes/enfold/config-templatebuilder/avia-template-builder/php/shortcode-template.class.php:1199
Stack trace:
#0 /www/wp-content/themes/enfold/config-templatebuilder/avia-shortcodes/av-helper-slideshow.php(354): aviaShortcodeTemplate::set_frontend_developer_heading_tag(”)
#1 /www/wp-content/themes/enfold/config-templatebuilder/avia-shortcodes/av-helper-slideshow.php(268): avia_slideshow->advanced_slide()
#2 /www/wp-content/themes/enfold/config-templatebuilder/avia-shortcodes/slideshow_fullsize/slideshow_fullsize.php(917): avia_slideshow->html()
#3 /www/wp-content/themes/enfold/config-templatebuilder/avia-template-builder/php/shortcode-template.class.php(633): avia_sc_slider_full->shortcode_handler(Array, Array, ‘av_slideshow_

Enfold is updated to the most recent version, so are all the plugins.
The error persists when all plugins are deactivated.
The error disappears if another theme is activated.
Other pages can be modified, also the french version of the same page can be modified.

Line 1199 of the file /www/wp-content/themes/enfold/config-templatebuilder/avia-template-builder/php/shortcode-template.class.php is:
static public function set_frontend_developer_heading_tag( array $atts, $meta = array() )

Line 354 of the file /www/wp-content/themes/enfold/config-templatebuilder/avia-shortcodes/av-helper-slideshow.php is:
dev_tags = aviaShortcodeTemplate::set_frontend_developer_heading_tag( $this->subslides[$key][‘attr’] );

Can you help us figure out where the problem is?
Login credentials below.

Thanks!