I have a archive page that shows all post types of a specific custom post type. That archive page also have children pages, and all the pages permalinks are now broken. The Custom Post type permalinks work fine.
For example:
/events/about-the-events/ - is a page
/events/an-actual-event/ - is a custom post type
/events/ is the archive page, /about-the-events/ is the child page, /an-actual-event/ is an event custom post type.
The Custom post type link works fine, while the child page is not found.
I am using /%postname%/ as permalink structure.