When leaving the labels at their default (blank), the admin submenu under the post type says Add New Post, rather than Add New ‘Postype Name’, which i think was working previously, but perhaps it’s somehow defaulting to the placeholder rather than the posttype name?
I just tested this and when adding a new post type after I enter the name and enable advanced settings ACF auto populates the labels.
More than likely there is a JavaScript error on your site that is preventing this from happening. I would start by looking at the console log to see if there is an error and try to correct it.
