ACF block preview: acf_register_block_type > 'example' array crash editor in WordPress 5.9.3

I use ACF block and add block preview box (the small floating preview box when mouseover block name in "Toggle block inserter" dialog). I use the code in the "Adding block previews" section in this doc:

https://www.advancedcustomfields.com/resources/acf_register_block_type/

Everything worked fine in WordPress 5.8. After upgrade WordPress to 5.9.3, the editor crashes when mouseover block name in "Toggle block inserter" dialog:

"The editor has encountered an unexpected error."

TypeError: b is not iterable
at /wp-includes/js/dist/block-editor.min.js?ver=54657317be78fb1c246c72b38dc2ed0e:7:34730
at Object.wh [as useMemo] (/wp-includes/js/dist/vendor/react-dom.min.js?ver=17.0.1:109:150)

I found that if I remove 'example' array inside acf_register_block_type, it won't crash. But this way block preview can't work.

'example' => array( 'attributes' => array( 'mode' => 'preview', 'data' => array( 'is_example' => true ) ) )

I'm using the latest ACF Pro Version 5.12.2

Please help if there's any solution to fix it. Thanks a ton!

Start with the “Adding block previews” example in the acf_register_block_type documentation and reproduce the crash in the WordPress 5.9.3 block inserter using ACF Pro 5.12.2. Investigate the interaction between the example attributes and the reported block-editor.min.js error; done means the inserter opens without an error and the block preview still appears.