I just updated to WordPress 5.5 and $is_preview is no longer working, as mentioned above.
This is a critical error – resulting in all ACF blocks no longer working on the front-end of the site.
How do we fix this?
I’d like to second this – without the width option I can’t usually use the clone field as it doesn’t work in the layouts I’m creating.
+1 from me as well.
The lack of this feature makes the clone field mostly useless to me unfortunately.