What is the Problem with IP addresses of subdomains on VPS/ISPmanager?

Question

Computer networks

Initial info:
Server Linux VPS Apache Centos
Single IP address, DNS on my domain 1ns.moydomen.ru/2ns.moydomen.ru, ISPmanager
5lite did not have. I "created" domains (on a whim) in the "Domain names" section, they automatically appeared in "WWW domains" for different Users. Here I had to buy a couple of domains. Did it as usual. Brought the user under them. Created in "Domain names" - everything works. Subdomains are required. I create test.novdomen.world in "Domain names" And began...
PROBLEM.
Subdomain - The browser cannot find the IP address of the subdomain. I am in support of the server (but on a dedicated VPS), they almost do not advise on the settings. I started to google and it turned out that all subdomains are created in the "WWW domains" section. I removed all the test subdomains created in the Domain Names section and created test subdomains in the WWW Domains section. In the "Domain Names" section of the main domains, A records of test/www.test simply appeared. But the subdomain does not open. I decided to check with www - opened three times and stopped opening.
The MAIN misunderstanding is that the subdomain was opened from the fifth time (during diagnostics -ok / ok / ok) Here it is on the network, I do a reboot, it disappears Diagnostics:
Lookup IP address information (ns1.moydomen.ru): [FAIL]
IP address : [FAIL]
Error:

What could be the reason A) sees the new IP domain, but its subdomain (all A records are available)? B) What could be the reason for this "floating" subdomain availability? If it didn't open at all, it would be understandable. And then, 2 times (after all cache cleanings and reboots) out of 15 attempts it opens. And it shows different diagnostics, then OK then {FAIL}
Help me figure it out-))

Answer 1

Understood. The case is one in 1000, but maybe someone will come across. The domain was purchased from a hoster. When problems with the subdomain started, I contacted them and they created all records in my account with their ns1/. It turned out that there are only DNS in the Personal Account, and others on the VPS server. So the trick went. I went to the personal account and deleted all records from the domain and everything worked.

Answer 2

add test.novdomen.world in WWW domains.
Domain names are DNS zones.