Since ACF v.6.3 update, the inner hierarchy of the Guttenberg Editor’s acf/wpo-acf-blocks changed so that there are two .acf-block-preview > .acf-block-preview elements in each block now.
Please refer to the attached screenshot.
Hey there,
We’re aware of this issue and have it on our backlog. It only affects the legacy version 1 of ACF Blocks, so if you upgrade to v2, you’ll be good as this wrapper doesn’t exist in ACF Blocks v2 – but we’ll have it fixed up in a future release if you don’t want to change.