I am facing an issue with "Custom Rewrite Slug" in custom post types.
The former developer structured data simply by using pages and categorizing them without organizing them into CPTs, but that method has its limitations. He made 2 parent pages (slugs: studies, universities) and subpages (i.e. /studies/economics/ , /universities/yale/ etc.)
I transferred the data to 2 CPTs (slug: study, university), and kept the 2 main pages (slugs: studies, universities). I also want to preserve the previous link structure (/studies/[page-slug], /universities/[page-slug]), because of SEO. I put the subpages to trash and gave custom slugs to the individual CPTs (/studies/, /universities/). But it doesn't work. When I use the original slugs (study, university) it works, but when I put studies or universities to the Custom Rewrite Slug field in Metabox, not. It throws out "Page not found."