Are you saying that you should be getting an array of post objects and that you’re getting an array of post IDs?
If this is the case, the most common cause of ACF returning ID values rather that posts, attachments, and other objects is a pre_get_post filter that is filtering queries that it shouldn’t be.
Deactivate other plugins, switch themes and see if you can narrow down the cause. I can tell you that I am not experiencing this on any of the sites I maintain and I’m not having this issue on my current project.