HTTP requests stops working after some time - http

Question

I have strange problem with my Game written in Unity (Mono). I have login functionality and then, after successfull login i'm sending some kind of keep-alive requests to ensure token is updated (I'm sending it every 30s).
The problem is, that after some time (sometimes it's 1 hour, sometimes 2.5 hours) all my requests have timeout status.
To be sure about my connection status I made some checks in code: I'm making simple GET to http://google.com and to main website of my API (not an API call. Just website GET). When I got timeout on API next time i figured out that:
After 1 timeout I have it always. Restarting application helps
I'm getting timeouts on API call and on GET request for base API website
Google is still responding with status 200 (no timeouts here)
Implementation:
On beginning i've been using RestSharp to handle requests, but the problem occured and there was a decision to throw RestSharp away and now we're using classic WebClient
class BetterWebClient : WebClient
{
private WebRequest _Request = null;
public TimeSpan? Timeout { get; set; }
protected override WebRequest GetWebRequest(Uri address)
{
this._Request = base.GetWebRequest(address);
if ( Timeout.HasValue )
{
_Request.Timeout = (int)Timeout.Value.TotalMilliseconds;
}
else
{
_Request.Timeout = 10*1000; //10s
}
if (this._Request is HttpWebRequest)
{
((HttpWebRequest)this._Request).AllowAutoRedirect = true;
}
return this._Request;
}
}
My HandleRequest function (which also calls Google and API website) looks like this:
public static void HandleRequest<TR>(string url, RestResponse<TR> executeGetRequest) where TR : new()
{
using (BetterWebClient w = new BetterWebClient() {Timeout = TimeSpan.FromSeconds(2)})
{
try
{
string downloadString = w.DownloadString("http://www.google.com");
Debug.Log("Google request: OK");
}
catch ( Exception )
{
Debug.LogError("Google request failed");
}
try
{
string downloadString = w.DownloadString("myAPIwebsite");
Debug.Log("WorldOfRescue.com request: OK");
}
catch ( Exception )
{
Debug.LogError("WorldOfRescue.com request failed");
}
}
var client = new BetterWebClient() {Timeout = TimeSpan.FromSeconds(5)};
client.Headers.Add("Accept", "application/json");
client.Headers.Add("Content-Type", "application/json");
try
{
string downloadString = client.DownloadString(url);
Debug.Log("Request for "+url+ " completed. Response: " + downloadString);
}
catch ( WebException e )
{
Debug.Log(e.Status);
throw;
}
catch ( Exception e )
{
Debug.Log(e.ToString());
throw;
}
finally
{
client.Dispose();
}
}
Do you have any idea why it happens? It looks like something is blocking me to send request to specific website, but in same time other website is working fine.