With latest version on ACF pro (and WP), I cannot show flexible fields correctly into pages that has the same base-slug of a custom post type. For example, if my post type is called “hero” (post type has no archive set, so no “hero” archive page with that slug) and I create a page with example.com/hero/ slug, in that page it doesn’t show flexible content correctly. If i change the slug of the page, it works (in fact on all website pages work except for these).
The problem related to flexible seems to be a bit complex. In fact it always show the first related box even if it’s not selected. Have a look at what you seen in frontend (attachment 1) and backend (attachment 2).
While, if you change -slug- into something else (for example trattamentiA), everything goes fine (attachment 3)