I'm having this same issue and have a ticket open with cloudflare enterprise support -- started this morning just after cloudflare performed maintenance on their DNS. No response from ENT support yet.
Opening a ticket with netlify too. for now i've simply put a cloudflare page rule up to bypass cache.
Got confirmation from cloudflare support that the `hello` response originated from netlify. netlify support predictably blamed cloudflare without any proof.
confirmed to be a netlify issue and should be resolved