If you use `dig` instead of `nslookup`, you'll be able to see which datacentre returned the reply. The authoritative servers may be overloaded or rate limiting queries from particular source IP addresses, occasional timeouts happen, and sometimes they result from overly strict or poorly considered rate limits on the authoritative side. Here's a sample `dig` query from LA, which enables the "NSID" EDNS option to report the datacentre location:
$ dig +noall +nsid +comment +ans -t a advego.com @8.8.8.8
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 8208
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
; NSID: 67 70 64 6e 73 2d 6c 61 78 ("gpdns-lax")
;; ANSWER SECTION:
advego.com. 94 IN A 89.208.226.140