[ERROR] Network.Socket.sendBuf: resource vanished

A web handler threw an exception. Details:
[timestamp1] Exception leaked to httpSession during phase 'sending-response':
During processing of request from xxx:
request:
"POST /parse HTTP/1.1\........"
A web handler threw an exception. Details:
Network.Socket.sendBuf: resource vanished (Broken pipe)
[timestamp2] Exception leaked to httpSession during phase 'user handler':

A bunch of similar errors are seen while running the duckling server.

Any inputs on why this might be happening?
Same request works intermittently.

Any help would be greatly appreciated,
Thanks