Synchronise websocket message among 3 server instances

Question

I'm new to websockets and I have implemented websocket using SignalR everything works fine in local and test environment but doesn't work in production the reason is in prod I have 3 instances and due to that sometimes I don't get the message if user is connected to 1 instance and the message is sent from another instance. How can I synchronise the messages considering the budget constraints too. I'm currently using azure SignalR free version but it's unreliable and I cannot even test it too. Is there anything which I can try? I'm using.net for backend and front end react. And using asp.net SignalR feature and azure app service.