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Big question here is, are any other tools giving 5XX errors on those PDF URLs (ending in .pdf) or just Moz on its own? Moz is known to have issues crawling URLs which contain certain characters, which other crawlers may not have a problem with - so you need a second opinion here Install this on Chrome: https://chrome.google.com/webstore/detail/redirect-path/aomidfkchockcldhbkggjokdkkebmdll?hl=en (mainly for tracking redirects, but also tells you status info in a handy way from a pop-out button) Visit one of the URLs directly which Moz is saying gives a 5XX. Does it on Chrome? Note: sometimes a page will look like it has rendered properly, but for some reason the server will still send an invisible 5XX response - this Chrome plugin would pick that up!) Also check the URL with this second plugin: https://chrome.google.com/webstore/detail/seo-indexability-check/olojclckfadnlhnlmlekdihebmjpjnoa?hl=en-GB If both those plugins agree the page loads fine on a 200, then Moz has an error. If they both agree that the page is a 5XX even though it looks legit, then you have a server response error If you get mixed results we have a mystery to look deeper into...