Have you updated to 5.07? Seemed to solve issues for me.
I am having the same issue. You are not alone 🙂
There’s a link to 5.04 by @Etic earlier in this thread.
Hi, you can’t create custom post types with ACF but you can simply use something like Custom Post Type UI plugin.
You can relate post types to each other using the relationship field and so allocate speakers to an agenda item when creating/editing an agenda post.