通过Gateway访问服务，服务出现异常但Sentinel没有触发熔断降级

通过Gateway利用Jmeter访问某个服务，出现内部异常，返回code:500，但是Sentinel没有触发熔断降级，满足每秒请求数>=N的要求，也满足异常数大于设定值的要求，异常没有被统计在异常数内？此情况下怎样能统计服务出现的异常？

Start by reproducing the Gateway request with JMeter and inspect how Sentinel handles the service's HTTP 500 response against the exception-count threshold. Determine whether the failure is counted for circuit breaking and document the configuration or behavior needed to count it; the payload names no source file or test to begin with.

Written by the indexing model from the issue text.