Titanium web proxy can't get response from long processing request

When I send POST request, which is taking over 60 second to return response Titanium proxy seems to fail. Instead proper response, after exactly 60 seconds from sending request I can see in Visual studio output window this message:

1610977002451   addons.productaddons    INFO    sending request to: https://aus5.mozilla.org/update/3/GMP/46.0.1/20160502172042/WINNT_x86-msvc-x64/pl/release/Windows_NT%2010.0.0.0%20(x64)/default/default/update.xml
1610977002464   addons.productaddons    INFO    Completed downloading document
1610977002464   addons.productaddons    ERROR   Request failed certificate checks: [Exception... "Certificate checks failed. See previous errors for details."  nsresult: "0x80070057 (NS_ERROR_ILLEGAL_VALUE)"  location: "JS frame :: resource://gre/modules/CertUtils.jsm :: validateCert :: line 113"  data: no]

I found property ConnectionTimeOutSeconds in Documentation, but this doesnt solve my issue. To make things clear, this is how I create proxy server:

var proxyServer = new ProxyServer(userTrustRootCertificate: false);
var explicitEndPoint = new ExplicitProxyEndPoint(System.Net.IPAddress.Any, 0, true);
proxyServer.AddEndPoint(explicitEndPoint);
proxyServer.ConnectionTimeOutSeconds = (int)TimeSpan.FromMinutes(15).TotalSeconds;
proxyServer.Start();

Any ideas how can I solve this?