Hi all,
Unfortunately this is a known issue between Gutenberg and ACF.
The issue was raised with the Gutenberg team who will look into a solution for WP 5.0.1.
We have mentioned this issue along with some other known ones in our latest blog post here. Please be sure to have a read: https://www.advancedcustomfields.com/blog/the-night-before-gutenberg/
You can follow the GitHub issue with WP here: https://github.com/WordPress/gutenberg/issues/12571#issuecomment-443984858
Thanks for your patience whilst we sort out these issues with the WP team.
