I was able to find the issue. You had set up your page to use the "ContentOrderBy" column when linking between pages.
That column is used for ordering the content on the page and can't be used reliably for linking since it can change when the content is re-ordered. It isn't a permanent value.
I updated your results and details pages to use the ContentID column instead and that should fix your issue for the long term. You should re-generate your sitemap.xml file and re-submit it to google in order to get the new links indexed, but you shouldn't have this problem anymore.... unfortunately older links won't work.