I can't update settings for certain custom post types (on my site, these have the slugs maintenance and emergency-sops)
Error message when trying to save is: You cannot use this slug because it is already used or a reserved word. Please choose a different slug.
All I am trying to do is turn on the "Author" field. I've just successfully done this for a number of other post types, and it worked fine. I've tried deactivating all plugins bar Toolset and reverting back to 2019 theme with no success.
During testing on my own website, I noticed that this message shows on the post type edit screen when a page with the same slug as the post type exists.
On your website too, I found these two pages, which have the same slug, as the two post types:
1. hidden link ( same slug 'maintenance' as the post type "Maintenance Tasks")
( hidden link )
2. hidden link ( same slug 'emergency-sops' as the post type "Emergency SOPs")
( hidden link )
To avoid this, you can either update the slug of these pages or the post type slugs to something different.