run PHP7.1.16 (64-bit) in FastCGI mode under Windows 2008R2 IIS7.5, and sometimes return a 502 error. Check the resource monitor and find that the php-cgi process cannot reside in memory, and the request is terminated at the end of the request.
maximum number of requests for instances: 1000, maximum number of instances: 100, activity timeout: 60, environment variables: PHP_FCGI_MAX_REQUESTS=1000;
php.ini:max_execution_time = 60 makeshift inputtimeout time = 60

Test script:
for / l% an in (1100) do curl conversion of http://localhost/phpinfo.php
to php7.0.29 (64-bit) is still a problem.

PS: tries Windows 2012, just like PHP5.6, it is normal under Windows10.