This is a performance issue. Optimize the _WS_Send() function in WebSocketAsio.au3 this way:
Func _WS_Send($sData)
Return DllCall($hWEBSOCKDLL, $c_ret_size_t, "websocket_send", "wstr", $sData, "USHORT", StringLen($sData), "BOOL", 0)[0]
EndFunc
Other functions involved in asynchronous callback must be similarly optimized.
Also remove the Sleep(10) line in the For loop in reproduce.au3.
It's exactly the same problem as in the Subclassing bug.