SignalR (original) does not send messages to client - signalr

Question

We're using SignalR (the original, not the Core version) and notice some inexplicable behavior. Our situation is as follows:
We have a Hub that accepts commands via a GenericCommand() method (see below).
These commands get placed on a messagebus using NServiceBus
The execution of the command yields an event
The handler of the event results in a message sent to all SignalR clients (see below)
Using the debugger tools in Chrome to view the Websocket messages it becomes clear that sometimes (but not always) the "InvokeToAll" message is never sent to any of the clients. No error is thrown and all clients that are connected just send their heartbeat signals indicating they are connected still.
Also, the tracing (see below) logs on the server indicate that the connection is clearly active the whole time, but for some reason the three test "Received" messages that are sent immediately from the hub are sent back to the clients, but the resulting "InvokeToAll" sent from the event handler are for some reason not sent using the Websocket. We know the event handler is called because the _notificationService.MarkAsDone() call leaves traces in the database confirming it's called.
One final thing we've noticed is that this setup works and works until it doesn't. As soon as the messages stop being sent to the clients, it stops for all clients at all time. We're completely at a loss as to what could possibly be happening or what else we can do to further debug this. No errors are thrown and something that works just suddenly stops working without notice...
Any help or pointers would be greatly appreciated.
Here's the code for the Hub (step 1):
public async Task GenericCommand(GenericEventData data) {
await _messageBus.PublishEvent(new GenericSignalrCommandReceivedEvent {
CorrelationId = Guid.Parse(data.CorrelationId),
Command = data.Command,
DataJson = data.DataJson,
ConnectionId = Context.ConnectionId
});
// Added for debugging purposes
var ctx = GlobalHost.ConnectionManager.GetHubContext<EventHub>();
IClientProxy proxy = ctx.Clients.Client(Context.ConnectionId);
await proxy.Invoke(data.CorrelationId, "Received - ConnectionId");
proxy = ctx.Clients.User(Context.User.Identity.Name);
await proxy.Invoke(data.CorrelationId, "Received - Clients.User");
proxy = ctx.Clients.Group("JCUSER:" + Context.User.Identity.Name);
await proxy.Invoke(data.CorrelationId, "Received - Clients.Group");
}
And here's the code for the event handler (step 4)
private async Task ReplyViaSignalR(SignalrCompletedData data, IMessageHandlerContext context) {
var ctx = GlobalHost.ConnectionManager.GetHubContext<EventHub>();
var proxy = ctx.Clients.All;
await proxy.Invoke("InvokeToAll", "Yay message received!");
await _notificationService.MarkAsDone(data);
}
Here's an excerpt from the trace log on the server for the connection of this client:
SignalR.Transports.TransportHeartBeat Information: 0 : Connection 1d603a67-1161-4a27-82f0-9046ec73cd60 is New.
SignalR.Transports.WebSocketTransport Verbose: 0 : Sending outgoing message. Connection id: 1d603a67-1161-4a27-82f0-9046ec73cd60, transport: WebSocketTransport, message: {"C":"d-498F7600-B,15|rS,0|pP,A|rT,1","S":1,"M":[]}
SignalR.Transports.WebSocketTransport Verbose: 0 : Sending outgoing message. Connection id: 1d603a67-1161-4a27-82f0-9046ec73cd60, transport: WebSocketTransport, message: {"C":"d-498F7600-B,15|rS,0|pP,A|rT,2|pR,1E","G":"F2q+KKxufchVxQUnH9leeyYR6fGPfHYRCIQW55XZbNEbbibRlbVYld/b0fzihC34VrDwmoaNy2uTJYnRCeQO9zGEoqNk+9qbAi72dPep52CgpicyPGQOlvNzUOlNK1v2j34SdPXHI8DwpDwx/7SA317XJMJPxrCE5Qsgt/kgTzE=","M":[]}
SignalR.Transports.TransportHeartBeat Verbose: 0 : KeepAlive(1d603a67-1161-4a27-82f0-9046ec73cd60)
SignalR.Transports.TransportHeartBeat Verbose: 0 : KeepAlive(1d603a67-1161-4a27-82f0-9046ec73cd60)
SignalR.Transports.TransportHeartBeat Verbose: 0 : KeepAlive(1d603a67-1161-4a27-82f0-9046ec73cd60)
SignalR.Transports.TransportHeartBeat Verbose: 0 : KeepAlive(1d603a67-1161-4a27-82f0-9046ec73cd60)
SignalR.Transports.WebSocketTransport Verbose: 0 : Sending outgoing message. Connection id: 1d603a67-1161-4a27-82f0-9046ec73cd60, transport: WebSocketTransport, message: {"C":"d-498F7600-B,1F|rS,5|pP,19|rT,2|pR,43","M":[{"H":"EventHub","M":"a1ec2fa6-f33c-4161-9166-07ee64558be1","A":["Received - ConnectionId"]},{"H":"EventHub","M":"a1ec2fa6-f33c-4161-9166-07ee64558be1","A":["Received - Clients.User"]}]}
SignalR.Transports.WebSocketTransport Verbose: 0 : Sending outgoing message. Connection id: 1d603a67-1161-4a27-82f0-9046ec73cd60, transport: WebSocketTransport, message: {"C":"d-498F7600-B,1F|rS,5|pP,19|rT,2|pR,44","M":[{"H":"EventHub","M":"a1ec2fa6-f33c-4161-9166-07ee64558be1","A":["Received - Clients.Group"]}]}
SignalR.Transports.WebSocketTransport Verbose: 0 : Sending outgoing message. Connection id: 1d603a67-1161-4a27-82f0-9046ec73cd60, transport: WebSocketTransport, message: {"I":"4"}
SignalR.Transports.WebSocketTransport Verbose: 0 : Sending outgoing message. Connection id: 1d603a67-1161-4a27-82f0-9046ec73cd60, transport: WebSocketTransport, message: {"C":"d-498F7600-B,1F|rS,5|pP,19|rT,2|pR,45","M":[]}
SignalR.Transports.TransportHeartBeat Verbose: 0 : KeepAlive(1d603a67-1161-4a27-82f0-9046ec73cd60)
SignalR.Transports.TransportHeartBeat Verbose: 0 : KeepAlive(1d603a67-1161-4a27-82f0-9046ec73cd60)
SignalR.Transports.TransportHeartBeat Verbose: 0 : KeepAlive(1d603a67-1161-4a27-82f0-9046ec73cd60)

Answer 1

As it turns out, this problem was caused by the fact that we have multiple sites in the same application pool pointed at the same directory using different host names.
This caused the application to run multiple concurrent instances of this site despite only showing one w3wp.exe process (which is what we looked at to dismiss the possibility of multiple instances running at once).
We plan to change this situation by simply combining the bindings to the same website instance when we have the opportunity. I fully expected the problem to be solved then.