Problems using Origin TLS certs

I've always used certs created by certbot but learned they are not recommended if you use CF proxy. I recently converted my nginx config to use the origin certs from the CF dashboard. My website login page looks normal but as soon as I try to login it returns Failed to load resource: the server responded with a status of 520 () and Response Status Error Code 520 from /login. This is very confusing to me as this endpoint either returns 401 if you have the wrong credentials or 200 if it logs you in. What could this be?
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