Thanks for the log. It looks like your application is repeatedly calling SAMLServiceProvider.InitiateSSO.
I suggest setting a breakpoint on the call to SAMLServiceProvider.InitiateSSO and following the code flow to see why this method is being called repeatedly.
The flow should be:
1. Call SAMLServiceProvider.InitiateSSO to create and send a SAML authn request to the IdP.
2. Login at the IdP.
3. Call SAMLServiceProvider.ReceiveSSO at your assertion consumer service endpoint to receive and process the SAML response.
Make sure the assertion consumer service endpoint is accessible. For example, in a WebForms application include a web.config in the SAML folder that includes:
<!-- No authorization for the SAML pages -->
<allow users="*" />