A 1200 error is a Cloudflare-specific error code for:
"The server isn't keeping up with Cloudflare's requests to it."
There are too many requests queued on Cloudflare's edge that are awaiting process by your origin web server. This limit protects Cloudflare's systems.
Tune your origin web server to accept incoming connections faster. Adjust your caching settings to improve cache-hit rates so that fewer requests reach your origin web server. Reach out to your hosting provider or web administrator for assistance.