We have two separate AD domains, both seeing the same problem.
there is a 2012 direct access server that has been working great - but we had to move to a new datacenter and have all new ip addresses. So we simply changed the external ip address in use on the DA server, and updated the external DNS name to match. Pretty straightforward. Now no clients are connecting.
I have tried changing the name in the directaccess configuration so it would rewrite the gpos, and then changing it back, once again updating the gpos. Applying this to a fresh new machine does nothing - still doesn't connect - so it's not only existing DA clients that are not working.
I sincerely hope this is not yet another oversight on Microsoft's part.