Hi. I am using ACF 3.9.0 and Gutenberg 3.9.0. Also WP 4.9.8 running the Genesis Monochrome Pro 1.0.1 theme. I have a checkbox field group that is not saving data when used in a normal post. If I activate the Classic Editor plugin (version 0.4), the post saves without any problem.
I searched through forum posts and while I found something similar, it was for earlier versions of both ACF and the Gutenberg plugin.
Any help anyone could offer would be greatly appreciated!