Gutenberg Additional CSS: Error loading gallery

Hi. Good work, very useful plugin!

I have WP 5.3 with native Gutenberg editor and have conflicts when I try too add a custom classes in Advanced > Additional CSS Classes
My class is only limiting te width { max-width: 1000px; }

In admin page, when I write the first characters in Additional CSS Classes field, inmediatly the FooGallery block throw this: Error loading gallery: Invalid parameter(s): attributes.
In front-end the gallery looks fine, but without my custom class.

Any idea? Thanks!