Updated PHP 8.4.15 to 8.5.0 IIS on Windows Server 2022 only one site can be used

[AlbertWeterings]

Description

I updated PHP 8.4.15 to 8.5.0 IIS on Windows Server 2022

When I open the first PHP site it works, after opening the first site all other sites throw html error 500
After restarting the ISS server I can again open 1 random site on the server after this other previously working sites again report same HTML error 500

Any PHP code

Resulted in this output:

Detailed Error Information:
Module FastCgiModule
Notification ExecuteRequestHandler
Handler PHP-850
Error Code 0xfffffffe
Requested URL [https://domain.com:443/phpinfo.php](https://domain.com/phpinfo.php)
Physical Path I:\inetpub\domain.com\www\phpinfo.php
Logon Method Anonymous
Logon User Anonymous

But I expected this output instead:

Multiple sites working on the same server

PHP Version

PHP 8.5.0 (cli) (built: Nov 18 2025 08:16:50) (NTS Visual C++ 2022 x64)
Copyright (c) The PHP Group
Zend Engine v4.5.0, Copyright (c) Zend Technologies
    with Zend OPcache v8.5.0, Copyright (c), by Zend Technologies

Operating System

Microsoft Windows Server 2022 Datacenter [10.0.20348] - Visual C++ 2022
Observation PHP < 8.5.0 is starting in taskmanager multiple instances of CGI / FastCGI where PHP 8.5.0 is only starting 1
FastCGI settings for PHP 8.5.0 is C:\PHP\php-cgi.exe max. Instances 4 Instance Max. Requests 1000

Disabling all extensions does not change anything.
Tested with:
php-8.5.0-nts-Win32-vs17-x64.zip
php-8.5.0-Win32-vs17-x64.zip
php-8.5.0-nts-Win32-vs17-x86.zip
php-8.5.0-Win32-vs17-x86.zip
All result in the same behavior

My temporary solution is changing the Application Pool Identity from NetworkService to ApplicationPoolIdentity don't know if this is the right way to solve the issue?

[iluuu1994]

@cmb69 Can you advice about what settings to use for IIS?

[cmb69]

I guess there is a problem regarding OPcache; see https://www.php.net/manual/en/opcache.configuration.php#ini.opcache.cache-id for a possible solution. Or maybe for testing, just disable OPcache at all.

[github-actions]

No feedback was provided. The issue is being suspended because we assume that you are no longer experiencing the problem. If this is not the case and you are able to provide the information that was requested earlier, please do so. Thank you.

[pom-wandries]

We have the same issue.
@iluuu1994, which IIS settings do you need?
The solution of @cmb69 is working for us.

Our operating system
Windows Server 2022 Datacenter 21H2

PHP 8.5.4 (cli) (built: Mar 10 2026 23:29:54) (NTS Visual C++ 2022 x64)
Copyright (c) The PHP Group
Built by The PHP Group
Zend Engine v4.5.4, Copyright (c) Zend Technologies
with Zend OPcache v8.5.4, Copyright (c), by Zend Technologies