the php-cgi terminated after requesting on php 7.x via fastcgi in iis 7.5

I run php 7.1.16 (7.0.29) via fastcgi in iis 7.5, sometimes get 502 errors, i found the php-cgi terminated after requesting in resources monitor.

running environment: windows 2008 r2 + iis 7.5 + php 7.1.6 (7.0.29) x64

fastcgi configuration: maxInstances=100, InstanceMaxRequests=1000, PHP_FCGI_MAX_REQUESTS=1000

test script: for /l %a in (1,1,100) do curl http://127.0.0.1/phpinfo.php

the phpinfo.php:

<?php
phpfino();