Since the WP 4.5 update, I am having a similar problem. Perhaps I can elaborate. I am using a WordPress theme called “Pangaea” which uses something called “Brad Page Builder” as simplified way to design the pages. It’s the proprietary page “builder” from the guy (Brad) who created the theme (however is no longer actively supporting it).
Here is where there is info on the HTML version, however I am using the WordPress version, which is no longer available for purchase, but this should give you an idea.
With the update of WP4.5, the Brad Page Builder interface never loads, but only shows a spinning circle that says, “Loading… please wait…” and it does so for literally, an hour, and never loads. Now I cannot edit any of my pages! I need the Brad Page Builder to load in order to edit the website.
Any insight would be GREATLY appreciated!