i've seen phantom latency when enabling cache rules. by default cloudflare doesn't cache JSON responses, so you need a cache rule to have it respect Cache-Control headers.

my latency to US east is around 200ms. putting cloudflare in front of it has negligible cost. enabling a single cache rule on a specific path added anywhere from 300-600ms latency on every route, just completely untenable.

tried it again recently and it seems to be fixed, but it was pretty frustrating couple weeks trying to debug what was wrong in the first place.