No I think it might be something to with certificates cause I had same issue when using curl commands and then I added --ssl-no-revoke and it started to work.
Anyway turned away from ClientSDK to code below and it works fine:
var client = new HttpClient();
var request = new HttpRequestMessage();
request.Method = new HttpMethod(“GET”);
request.RequestUri = new Uri(“https://paper-api.alpaca.markets/v2/account”, UriKind.RelativeOrAbsolute);
var response = await client.SendAsync(request);
var content = response.Content.ReadAsStringAsync();