Since WordPress 5.6, the block editor has a new version of the Block API. The ACF 5.10 release introduced support for the Block API v2. This is only available when ACF is installed on sites using WordPress 5.6 and above.
The block wrapper element for ACF Blocks with Block API v2 support now have a predefined class of
name is generated from the name of the block. This is in line with the changes to how the block editor defines the default wrapper element.
<div id="testimonial-block_6126540e5e5e2" class="testimonial wp-block-acf-testimonial">
In ACF 5.10 we moved to support version 2 of the WordPress Blocks API. The goal was to support more advanced functionality such as the ability to use the Block Editor’s
extraProps filter. Unfortunately, our implementation of this triggered re-rendering of ACF blocks anytime a property changed, which caused issues with other block editor features such as block styles and the built-in spacing/padding support.
ACF 5.11 removed support of the extraProps functionality to prevent these re-renders which will improve performance and solve issues with block styles. We want ACF blocks to function as closely as possible to core or custom-built WordPress blocks. Therefore, we’re working on re-introducing support for this in an upcoming release.