Upfront Editor not display sidebar (white sidebar)

Hi, the sidebar of the Upfront Editor on my website is not working and is showing as a white bar with no content. See screenshot below:

I followed the advise of Adam Czajczyk during the Live Chat Support session today (11 Jan, 2017) and added the following line to the wp-config of the site: define('WP_MEMORY_LIMIT','256M':wink:;

Unfortunately that did not help at all and Adam suggested I open a ticket and grant support access to my site (done).

Please advise how to resolve this problem.

Regards,

Georgi

P.S. If unclear – Support Access is Granted on the affected website.