If you change nameservers from Custom nameservers to our default ones or vice versa, the host records will not be added to the new nameservers automatically. Please make sure to save all the needed settings and set them up manually after the nameservers switch.
Nameservers changes do not propagate instantly. Once your nameservers are changed, it may take up to 24 hours (more, in rare cases) for local ISPs to update their DNS caches so that everyone can see your website.
You can always check your domain name using any Proxy server as Proxy servers do not store cache, thus you can see the non-cached information.