XenForo Cloudflare error 520 after login "Web server is returning an unknown error"

[drastic]

I randomly started getting error 520 on Cloudflare, with it saying "Web server is returning an unknown error."

I checked with the host, the devs, and now checking here to see if anyone knows how to fix it. The website functions fine, but when I try to login as a normal user, then it gives me that message. Screenshot attached. Thanks if anyone has a fix.

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