If an include page is not published (or accidentally unpublished) you get a 404 for all pages in the site

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This occurs in DXA 1.8, not yet tested in DXA 2.0.
The DXA could be made more resilient to these potential CMS user errors by simply not adding the include as a region to the page model if it cannot be found (or by adding an appropriate error entity, or both)