I think I need to write a [[sitelink]] shortcode or improve [bw_button] or both. I developed this website locally then migrated it using the simple steps I outlined in How to clone a local site to a hosted WordPress site. Apart from a strange problem with my child theme not being recognised (case sensitivity issue) the main challenge was in the links not having been updated in page content.
So, since I want to check each slide anyway, rather than faff around finding the plugin I should/could have used, I’m changing each invalid link as I come across them.