can't handle multiple request using rabbitmq and masstransist in .net core - asp.net-core

Question

I am currently working with micro service architecture and .net core.
Rabbit MQ + MassTransit are being used to send and receive data between the micro services.
I have a host application in IIS and from 2 separate browsers I send the same request to micro service and that microservice calls other service using RabbitMQ.
I expect to get 2 separate requests hitting the consumer but instead get an internal server error.
Startup:
services.AddScoped<OrderCompletedEventConsumer>();
services.AddMassTransit(x =>
{
x.AddConsumer<Controllers.OrderController>();
});
services.AddSingleton(provider => Bus.Factory.CreateUsingRabbitMq(cfg =>
{
var host = cfg.Host(new Uri("http://192.168.101.111:5672"),
"/", h =>
{
h.Username("Test");
h.Password("test");
});
cfg.ReceiveEndpoint(host, "TestQUE", e =>
{
e.Consumer<Controllers.OrderController>(provider);
});
}));
//Register Publish Endpoint of RabbitMQ bus service
services.AddSingleton<IPublishEndpoint>(provider => provider.GetRequiredService<IBusControl>());
//Register Send Endpoint of RabbitMQ bus service
services.AddSingleton<ISendEndpointProvider>(provider => provider.GetRequiredService<IBusControl>());
//Register Bus control for RabbitMQ
services.AddSingleton<IBus>(provider => provider.GetRequiredService<IBusControl>());
//Regster Bus Service hosting
services.AddSingleton<IHostedService, BusService>();
Request From One microservice:-
IRequestClient<IAddRequest<IOrder>, IAddResponse<IOrder>> orderClient =
new MessageRequestClient<IAddRequest<IOrder>, IAddResponse<IOrder>>(_bus,
EndpointAddress("orderQue"), TimeSpan.FromSeconds(Convert.ToDouble("150")));
var addResponse = orderClient.Request(new
{
entity = order
});
await Task.WhenAll(addResponse);
Consumer
public async Task Consume(ConsumeContext<IGetRequest<IOrder>> context)
{
// Operation and return result
await context.RespondAsync<IGetResposne<IOffice>>(new
{
// send result.
});
}
In the consumer the 2 separate requests from different browser arrive but both are unsuccessful. However if I do one request at a time then it will work, why is this?
Please give any idea, suggestion or hint.
Thank you,