Can not add content to accordions

Hi,

I can create accordions and 1 content accordion. But when I click “Add” for more content nothing happens. Tested it on localhost and online, both in Chrome and Edge. I’m working on PHP7.

I do see error in the console:
Uncaught TypeError: Cannot read property ‘length’ of undefined
at HTMLDocument.<anonymous> (post.php?post=169&action=edit:71)
at i (load-scripts.php:2)
at Object.fireWith [as resolveWith] (load-scripts.php:2)
at Function.ready (load-scripts.php:2)
at HTMLDocument.K (load-scripts.php:2)
2load-scripts.php?c=1&load[]=hoverIntent,common,admin-bar,heartbeat,autosave,suggest,wp-ajax-response,jquery-color,wp-lists,jquery-ui-core,jquery-ui-widget,j&load[]=query-ui-mouse,jquery-ui-sortable,postbox,jquery-ui-position,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete,tags-suggest,tags-box&load[]=,underscore,word-count,post,svg-painter,wp-auth-check,jquery-ui-draggable,jquery-ui-slider,jquery-touch-punch,iris,wp-color-pick&load[]=er,shortcode,backbone,wp-util,wp-backbone,media-models,moxiejs,plupload,wp-plupload&ver=4.9.1:343 Uncaught TypeError: Cannot read property ‘hasClass’ of undefined
at HTMLDocument.<anonymous> (load-scripts.php?c=1&load[]=hoverIntent,common,admin-bar,heartbeat,autosave,suggest,wp-ajax-response,jquery-color,wp-lists,jquery-ui-core,jquery-ui-widget,j&load[]=query-ui-mouse,jquery-ui-sortable,postbox,jquery-ui-position,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete,tags-suggest,tags-box&load[]=,underscore,word-count,post,svg-painter,wp-auth-check,jquery-ui-draggable,jquery-ui-slider,jquery-touch-punch,iris,wp-color-pick&load[]=er,shortcode,backbone,wp-util,wp-backbone,media-models,moxiejs,plupload,wp-plupload&ver=4.9.1:343)
at HTMLDocument.dispatch (load-scripts.php:3)
at HTMLDocument.r.handle (load-scripts.php:3)
at Object.trigger (load-scripts.php:3)
at Object.a.event.trigger (load-scripts.php:9)
at HTMLDocument.<anonymous> (load-scripts.php:3)
at Function.each (load-scripts.php:2)
at a.fn.init.each (load-scripts.php:2)
at a.fn.init.trigger (load-scripts.php:3)
at Object.<anonymous> (load-scripts.php?c=1&load[]=hoverIntent,common,admin-bar,heartbeat,autosave,suggest,wp-ajax-response,jquery-color,wp-lists,jquery-ui-core,jquery-ui-widget,j&load[]=query-ui-mouse,jquery-ui-sortable,postbox,jquery-ui-position,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete,tags-suggest,tags-box&load[]=,underscore,word-count,post,svg-painter,wp-auth-check,jquery-ui-draggable,jquery-ui-slider,jquery-touch-punch,iris,wp-color-pick&load[]=er,shortcode,backbone,wp-util,wp-backbone,media-models,moxiejs,plupload,wp-plupload&ver=4.9.1:4)

Any idea what’s wrong?