In 04.05 block alignment, if you set the block alignment, unset the block alignment, save the post and then reload the editor, the block will be broken and display This block has encountered an error and cannot be previewed.
This is the markup the block has:
<!-- wp:jsforwpblocks/block-alignment-toolbar {"className":"alignundefined"} -->
<div class="wp-block-jsforwpblocks-block-alignment-toolbar alignundefined message-body"><p>testiung testing 123</p></div>
<!-- /wp:jsforwpblocks/block-alignment-toolbar -->
I expect all it needs is the align class in the save method being wrapped in a conditional statement