@Loeya Thanks for raising it!
In fact, translate.kagi.com and kagi.com are hosted on two different Google Load Balancers. We don't try to block any IP from our firewall by default. These PINGs are blocked somewhere, either the China Great Firewall or the GCP Backbone, we're unsure, based on the output of the attached image.
We also have this similar with some VPN providers, VPN connected users sometimes are rejected with 403 response, but it's on HTTP (Layer 7).
We had contacted GCP for these issues, but unfortunately, it's not resolved yet.