Hello guys !
I had the same problem as you since Monday morning although I don't use the dotnet library from IG. I use two constructors from the dotnet framework in my LabVIEW program. The first is WebClient (it's a bit barbaric as a way of doing things, but it's been working well since 2015 even if Microsoft recommends using a more current solution: System.Net.Http.HttpClient ).
Its path is System (4.0.0.0)>System.Net>Webclient().
This constructor has a method named OpenRead which generates a Stream instance. Then I use the StreamReader constructor (the second constructor).
Its path is mscorlib(4.0.0.0)>System.IO>StreamReader(Stream,Stream).
This constructor takes as argument the Stream instance provided by the OpenRead method of the WebClient. Then just call the "ReadLine" method of the StreamReader in a loop.
I tell you my life to make it clear that with this very simple structure I had the same problem as you since this weekend. The stream server was rejecting me without even returning a response. But today I added in my program a call to the ServicePointManager property. The call to this property is done before the call to the WebClient constructor.
The System.Net.ServicePointManager class has the path :
System(4.0.0.0)>System.Net>ServicePointManager
and I assign it the value Tls12 (among the other values which are: SystemDefault, Ssl3, Tls, Tls11,Tls12, Tls13 and " others"). And the flow starts again. I don't use version 3 for the IG API and it still works. Hope this can help you!
Thank you for your various messages wich allowed me to find the way out of my problem. I hope this will also solve yours which seems to me to be of the same nature.
Thanks to Firefox and its Web Development tool in the IG Companion webpage (https://labs.ig.com/sample-apps/streaming-companion/index.html) .