Internet providers (ISPs) maintain a DNS name cache system to avoid repetitive requests and reduce the expense of unnecessary traffic on the network.
Therefore, when a page is found on services that use this system, there is a DNS lookup on the Internet and it is cached for a specified period for future similar requests.
This means that when we make a DNS change to serve the zone, these services continue to query the cached old DNS and access to the old address.
This cache is renewed, generally between 2 hours or up to 72 hours according to each provider, and can be extended depending on the consistency in which the previous server is used. The less use, the longer the propagation time. Even so, this may vary according to each established configuration.
It is not possible to do a "DNS change synchronization immediately", and it should not be considered as an error, but as a process of propagation from your current internet provider, which does not instantly update the changes from Server to Server, ( DNS). This is usually corrected automatically in an average of 24-72 hours.