Thank you so much @juliengemaddis for providing your code, it solved my issue, and I was struggling to figure it out. I had done just as you mentioned, left the 'core/list-item' out of my api call to allow_block_types hook
Hi Everyone, this has been a really painful bug for me as well. I kept reading replies. I think the answer is that ‘__return_false’ needs to actually return false, so I wrote an inline function and it worked for me on WordPress 4.5.3, Ubuntu Linux, and NGINX. I hope this helps!
I was able to resolve this by changing this line of code:
add_filter( 'big_image_size_threshold', '__return_false' );
to this:
add_filter( 'big_image_size_threshold', function(){ return false; } );
Best of luck!
