Interesting. The main validation seemed to work, but the secondary validation found an NXDOMAIN when looking up A (where I'm guessing it should be something like NOERROR if the name exists but there are just no A records for it?)
Can you double-check that all your authoritative DNS servers give consistent answers for both A and AAAA for that domain? I don't see any problems in my quick checking but I'm no DNS expert.
There's another post recently with a secondary validation error that doesn't seem to make much sense either. I don't know if that's enough to raise the red flag and say there's some consistent problem, though.
Have you just tried once, or is this problem repeatedly happening?