"The current DNS is unnecessarily slow and inefficient because of efforts to accommodate a few DNS systems that are not in compliance with DNS standards established more than a decade ago." The DNS flag day page says.
Now it's time to change it. So some of the main DNS gaints reach a consensus that we must drop the non-standard implements. That can influence your domain names.
Go to the page, and check whether your domain's DNS has been ready. If not, submit a service ticket to tell your nameserver provider.
I have tested CloudFlare DNS and DigitalOcean DNS. Both passed the test.
This is important. Since if your nameserver is not ready, your domain can stop working after the DNS flag day (Feb 1st, 2019).