Strange problems with nic.ru DNS hosting for 3rd level domains?

Question

Domain Name System

Domains are registered correctly, support confirmed it. For the old.site.com domain, “old A 1.2.3.4” is indicated,
periodically the domain starts to disappear from some dns servers in various places, and somewhere ok
The site.com second-level domain itself is always given without problems. The problem looks like this:

; <<>> DiG 9.8.4-rpz2+rl005.12-P1 <<>> old.site.com @tried everything here
;; global options: +cmd
;; got answer:
;; ->>HEADER<< - opcode: QUERY, status: NXDOMAIN, id: 5785
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:
;old.site.com. IN A

;; AUTHORITY SECTION:
site.com. 1 IN SOA ns3.nic.ru.

Support cannot help or does not want to, politely answer that users probably type www.old.site.com and offer to register also www.old, although I sent them the dig output. Is it treated somehow, except for changing the DNS hosting / registrar?

Answer 1

Without a zone file, it's hard to say anything specific.
I would venture to suggest:
maybe there are two entries in the file for the old subdomain (for example, A and then some NS). As a result DNS such stupidly ignores with WARNING'OM.

Answer 2

Support answered and I hope it helped - their old servers got into the list: ns3.nic.ru ns4.nic.ru ns8.nic.ru
removed them, we'll see.

Answer 3

moved to comment