Error Code: 0 ExceptionMessage: Http failure response for (unknown url): 0 Unknown Error in Angular 5

I am getting this error "Error Code: 0 ExceptionMessage: Http failure response for (unknown URL): 0 Unknown Error" on my Angular 5 project.

However, I am not able to recreate this issue, I saw this repeated issue on the Rollbar error log. I tried the same steps on my local machine, also tried to recreate in different browsers like chrome, safari, etc but no luck.

I'm using AWS lambda with .NET core 2.1, API proxy gateway, and Angular 5 on FrontEnd.

AngularJs code

getOrgPublicAssetName(id: number): Observable<any> {
    let content = this.appSharedService.getSitecontents();
    if (content !== '')
      return Observable.of(content);
    if (id !== undefined)
      return <Observable<any>>(
        this.httpClient
          .get(this.organizationUrl + '/SiteContent/' + id)
          .map(result => {
            this.appSharedService.setsitecontents(result);
            return result;
          })
          .pipe(catchError(this.exceptionService.catchBadResponse))
      );
    else return Observable.of();
  }

Following is my startup.cs configure function where I am already using cors.

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
        {
            app.UseXRay("Organizations");
            app.UseMiddleware(typeof(ErrorHandlingMiddleware));

            Environment.SetEnvironmentVariable(EnvironmentVariableAWSRegion.ENVIRONMENT_VARIABLE_REGION, Configuration["AWS:Region"]);

            // Create a logging provider based on the configuration information passed through the appsettings.json
            // You can even provide your custom formatting.
            loggerFactory.AddLambdaLogger(Configuration.GetLambdaLoggerOptions());

            //Enable swagger endpoint if the environment is not production

            if (!IsProductionEnvironment)
            {
                // Enable middleware to serve generated Swagger as a JSON endpoint.
                app.UseSwagger();

                // Enable middleware to serve swagger-ui (HTML, JS, CSS, etc.), specifying the Swagger JSON endpoint.
                app.UseSwaggerUI(c =>
                {
                    if (env.EnvironmentName == "Local")
                        c.SwaggerEndpoint(SwaggerLocalEndpoint, ApiName);
                    else
                        c.SwaggerEndpoint(SwaggerEndpoint, ApiName);
                });
            }

            app.UseCors(policy =>
            {
                //TODO: This has to be addressed once we deploy both api and ui under the same domain
                policy.AllowAnyOrigin();
                policy.AllowAnyHeader();
                policy.AllowAnyMethod();
                policy.WithExposedHeaders("WWW-Authenticate");
                policy.WithExposedHeaders("X-Total-Count");
            });
            app.UseAuthentication();
            app.UseMvc(routeBuilder =>
            {
                routeBuilder.Count().Filter().OrderBy().Expand().Select().MaxTop(null);
                routeBuilder.MapODataServiceRoute("odata", "odata", OrganizationModelBuilder.GetEdmModel());
            });
            app.UseForwardedHeaders(new ForwardedHeadersOptions
            {
                ForwardedHeaders = ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto
            });
            app.UseResponseCaching();
        }
    }