Javascript redirects are not recommended when using Prerender.io for SEO.
If you are doing a redirect, you want Google and other crawlers to know about the redirect so they can update their index to point to the correct page. The Prerender server tries not to follow redirects and instead looks for the prerender specific meta tags in order to give you the chance to tell crawlers that they should update their index.
Extra answer: The Prerender server counts the number of requests in flight in order to try to tell when the page has fully loaded. If you would like more control over that, you can tell the Prerender server to wait by setting window.prerenderReady = false; when the page initially loads. Then, when all of your ajax calls are finished, set window.prerenderReady = true; and the Prerender server will save the static HTML at that point.
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