Sites delegated to NS servers added to the list of child sites do not work. What is the reason?

Question

Domain Name System

After adding your NS servers to the registry of child ones, the sites that are delegated to them, for some reason, sometimes open for some people, sometimes they don’t.
And after cleaning the DNS cache, everything opens for them. It's been 5-6 days since it was added.
Before this, this was not the case.
What could be the reason? By the way, if that is worth the PowerDNS associated with MySQL

Answer 1

Subsidiaries often do not work. For the site to work, I recommend using CloudNS, creating A records and specifying the IP of the server. Performance is guaranteed.