I encountered this issue as well, and the comments above pointed me in the right direction.
I had registered my blocks using the acf_register_block() function, outlined in the documentation. I didn’t specify the mode, but that turned out to be the key to get this working. Setting the ‘mode’ to ‘edit’ was the first step, and ‘auto’ may have the same results. I also needed to convert the reusable block to a regular block, save the post, and reload the editor.
