On your Cloudflare account, if there was a change in the CNAME/A record being proxied vs. DNS only, that could cause an issue, as Cloudflare would then strip headers off the request that your Apache/Nginx would be looking for.
If you enabled HTTP DDoS protection in your Security -> WAF tab (I think that’s where it is) that could do this too. Might be worth disabling.
Also check for any headers your HTTP load balancer might be expecting, that Cloudflare could be stripping.
Might be worth tailing the webserver logs to see what happens to requests coming in from Cloudflare.
On your Cloudflare account, if there was a change in the CNAME/A record being proxied vs. DNS only, that could cause an issue, as Cloudflare would then strip headers off the request that your Apache/Nginx would be looking for.
If you enabled HTTP DDoS protection in your Security -> WAF tab (I think that’s where it is) that could do this too. Might be worth disabling.
Also check for any headers your HTTP load balancer might be expecting, that Cloudflare could be stripping.
Might be worth tailing the webserver logs to see what happens to requests coming in from Cloudflare.