Sorry to say, but thats a PHP/WordPress error, not a Cloudflare error. This is not related to Cloudflare at all.
Yes the A Record points to Cloudflare, that is the DNS. The DNS and its Proxy does not have anything to do with failed to send buffer of zlib output compression (1).
Just activate the Developer Mode or if you really want to make sure your server does not receive a request from Cloudflare, unproxy the DNS entries you need to call your page. Then AFTER this took effect test again.