Problem:
The user was not able to edit a page on the block editor. Each time he tries to add a block, the editor crashes.

Solution:
It turns out that the user was having an erroneous Reusable block.
Go to https://sina.modsnapstaging.com/wp-admin/edit.php?post_type=wp_block and remove(send to trash) the "Untitled Reusable Block" entry. Check this screenshot http://prntscr.com/uuou8w
Then you will be able to edit the homepage with the block editor.