https://libzmq.readthedocs.io/en/latest/zmq_msg_send.html

common/ZMQWrappers.cpp

@@ -95,10 +95,14 @@ bool ZMQSocket::SendZeroCopy(void *data, size_t size,void (*callback)(void *, vo
     }
 
     auto result = zmq_msg_send(&msg, socket, (blocking ? 0 : ZMQ_DONTWAIT));
-    zmq_msg_close(&msg);
 
-    if (result == size)
-        return true;
+    // https://libzmq.readthedocs.io/en/latest/zmq_msg_send.html
+    // zmq_msg_close only if it fails to send
+    if (result >= 0)
+        return true;  // msg is now owned by ZMQ — do NOT close it
+
+    // Send failed — we must close the message ourselves
+    zmq_msg_close(&msg);
 
     if ((errno == EAGAIN) || (errno == EINTR))
         return false;