Site content not fully loading when proxied

I have 3 websites on the same server, all routing through Cloudflare. One of those websites is having an issue where if I turn the proxy mode on in the DNS settings, the page will load, but most of the content does not. It’s just a Background image, a nav menu, and that’s it. But as soon as I switch proxy off, it loads just fine. I’ve checked it from other IPs using GeoPeeker, and the same thing happens. I also did a domain health test with MX Toolbox, and it returned an HTTP Connect error:

“HTTP Connect: Unable to read data from the transport connection: The connection was closed.”

https://mxtoolbox.com/problem/https/HTTP-Connect?page=health_https&hidetoc=0&hidepitch=0&showlogin=1&action=https:bibleburrito.com&domain=bibleburrito.com

I have no idea why only 1 or my 3 websites is doing this or how to correct it other than to turn proxy mode off. Obviously I would prefer to keep proxy on.