I am getting this exact same error years later. This is the stack trace. I hope it is okay to drag this topic up from the dead, but this was the only thing I could find based on what I am seeing. This is causing intermittent issues with the editor screen. Clickable items like “screen options”, “Visual Editor”, “Text Editor” do nothing.

Uncaught Error: cannot call methods on sortable prior to initialization; attempted to call method ‘toArray’
at Function.error (https://www.meridianhm.com/wp-includes/js/jquery/jquery.js:2:1814)
at HTMLDivElement.<anonymous> (https://www.meridianhm.com/wp-includes/js/jquery/ui/widget.min.js:11:2115)
at Function.each (https://www.meridianhm.com/wp-includes/js/jquery/jquery.js:2:2881)
at a.fn.init.each (https://www.meridianhm.com/wp-includes/js/jquery/jquery.js:2:846)
at a.fn.init.a.fn.(anonymous function) [as sortable] (https://www.meridianhm.com/wp-includes/js/jquery/ui/widget.min.js:11:1857)
at HTMLDivElement.<anonymous> (https://www.meridianhm.com/wp-admin/js/postbox.min.js:1:3165)
at Function.each (https://www.meridianhm.com/wp-includes/js/jquery/jquery.js:2:2881)
at a.fn.init.each (https://www.meridianhm.com/wp-includes/js/jquery/jquery.js:2:846)
at Object.save_order (https://www.meridianhm.com/wp-admin/js/postbox.min.js:1:3103)
at $.AviaBuilder.place_top (https://www.meridianhm.com/wp-content/themes/meridian/config-templatebuilder/avia-template-builder/assets/js/avia-builder.js:135:34)
error @ jquery.js:2
(anonymous) @ widget.min.js:11
each @ jquery.js:2
each @ jquery.js:2
a.fn.(anonymous function) @ widget.min.js:11
(anonymous) @ postbox.min.js:1
each @ jquery.js:2
each @ jquery.js:2
save_order @ postbox.min.js:1
place_top @ avia-builder.js:135
set_up @ avia-builder.js:118
$.AviaBuilder @ avia-builder.js:107
(anonymous) @ avia-builder.js:1376
i @ jquery.js:2
fireWith @ jquery.js:2
ready @ jquery.js:2
K @ jquery.js:2