It's been weeks since I last saw even a trace carrier at 6400, and some folks I know in anther forum, who copy that one better that I ever have, reported it missing. I have seen a mode right on top of that frequency at time, STANAG 4285 I believe (I'm no expert but that's what it looked and sounded like) during the hours I'm most likely to catch it, but these Europe based listeners have not copied that at all. Perhaps what you heard was from the same parties responsible?
EDIT 03/23/18 1245 z - Just before dawn in my QTH, the best time for Asian signals for me. No STANAG or anything else on 6400, and no broadcast either. I think this one is off the air, at least temporarily.