@rg305, I agree that the nameservers are sometimes giving problems, and that that could interfere with issuance of @KingChen's certificate—but I don't think that's the problem that he encountered here, because the error from Let's Encrypt would be different in that case. (When I re-ran the Let's Debug test, it was very slow, but it eventually succeeded.)
@KingChen, could you please clarify whether 139.217.112.174 is your own server, that you are the administrator of?