Not sure if this issue has been resolved. I am having a similar issue. I have created a custom post and added custom fields using ACF. When logged in as an admin, everything works perfectly but when one of my users logs in (Author or Editor roles), the custom fields did not save data. Looks fine on the page after Publish is clicked, but a refresh and the fields are empty. Title and featured image stay, but no custom fields. As with other suggestions I installed classic editor plugin and that has solved the problem for me. A shame not to be able to use Gutenberg but we will live with it.
