Answer:

Asn-345
The side chains of His, Asn, or Gln, sometimes need to be rotated by 180^o  around the second, second, third torsion angle in the side chain, respectively. And if such a flip is found by WHAT_CHECK, it will report it under this header.
Because the Asn O_δ  is pointing at an O_ε  of Glu-349. The Nδ of this Asn would be much happier if flipped with the Oδ.