What are connection reset, DNS poisoning and the others?
Four ways a request can be interfered with. A connection reset tears the connection down mid-request, so nothing arrives. DNS poisoning answers the name lookup with an address that is not the site's, so the request never reaches it. A redirect inside mainland China lands the request on a server in the country instead of the real one. Failure to load is the residual case: the control downloads the page, the mainland China probes cannot. Each is a filter on the Explore page, so you can see which addresses are affected by which.