Hi, are there some people experiencing issues on some AS when using iana blackhole nameservers for localnets?

I usually meet this response for instance: dig 172.16.1.1 @blackhole-1.iana.org ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 34667 ;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1 ;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;172.16.1.1. IN A

;; Query time: 46 msec ;; SERVER: 192.175.48.6#53(192.175.48.6) ;; WHEN: Thu Oct 27 16:

But I don't get any reply packet on AS8220 (COLT). dig 172.16.1.1 @blackhole-1.iana.org ;; global options: +cmd ;; connection timed out; no servers could be reached

thank you.