Intermittent 520 error through CloudFlare

For the last few days, my site has intermittently returned 520 errors. Refreshing the page usually works, though sometimes a page has to be refreshed multiple times. The website host says the issue is not them. They say “CF IP ranges are allowlisted on the server’s Firewall. The logs on our end do not indicate any connection issues. The apache of the server is up and running and there are no stuck processes”
If I set Cloudflare to Development Mode, then the site works fine. Please advise.

Actually, Development Mode doesn’t work either. Pausing the site on CF seems to though.