Quoting from the web site at https://dnsflagday.net/
What is happening?
The current DNS is unnecessarily slow and suffers from inability to deploy new features. To remediate these problems, vendors of DNS software and also big public DNS providers are going to remove certain workarounds on February 1st, 2019.
This change affects only sites which operate software which is not following published standards. Are you affected?
On that web page, there is a Domain Owner's test. I have already tested AMPR.ORG, and it passes except for one test on one of our secondary servers times out. I am working with the person who so kindly runs that secondary server [in Thailand] to get this fixed. Please don't run any more tests on the AMPR.ORG domain.
But if *you* operate servers for a subdomain of ampr.org, such as 'se.ampr.org', you may wish to test your subdomain and see if there are things you need to fix. In fact, the "se.ampr.org" subdomain does indeed have a few problems that probably should be addressed. (In particular, it looks like the DNS server software for that domain may not be listening on the IPv6 addresses for those servers.) - Brian