This used to work fine before. So its probably related to a WP update.
However its not a “gutenberg issue” but seems like a conflict (or maybe wordpress removed something?) between gutenber and ACF
Setting it to high didnt sort it for me.
I have created a super simple plugin for me to add a simple separator with text and description, to separate sections, as you are asking
Sorry for the spanish pics, is the site im currectly working on.