Problems with FastCgi in PHP v.7.1.7

Hello expert,

Recently, my websites running (on the same 32-bit webserver) under PHP version 7.1.7 crash many times (Internal Server Error 500),
or are ‘frozen’ in a process (Loading data…) which does not end.
The Internal Server Error is traced back to a FastCGI problems/failures.
Sometimes, refreshing the browser-window (F5 or ctrl-R) helps, but often I have to restart my webserver entirely (hard-reboot).

Error message:
“HTTP Error 500.0 - Internal Server Error. The FastCGI process has failed frequently recently. Try the request again in a while.”

A. Example Piwik:
Clicking on the webpages of Piwik, navigation towards a monitored website:
Piwik: Settings | Websites | Manage -->
Piwik-site page gets stuck in ‘Loading data…’ or displays error message:
“HTTP Error 500.0 - Internal Server Error. The FastCGI process has failed frequently recently. Try the request again in a while.”

The statistically calculated content of the Piwigo-site (visitor activities) is often blanc in Piwik detail-pages, and sometimes filled with appropriate data.

Example A - Piwigo (online photo album showcase):
Clicking in album categories of Piwigo
and on individual photo’s for detail-page cause this FastCGI error message.
This happens especially when handling GIF-animations, which are resized on the fly by the Imagick-plugin.
(The website also contains the PicLens 3D Wall plugin).
The Imagick-plugin in Piwigo needs C++ runtime:
This will not work in combination with the latest version: Microsoft Visual Studio C++ 2017 Redistributable (x86) 14.10.25017
This may work with: Microsoft Visual C++ 2015 Redistributable (x86) - 14.0.23026 , but often results in ‘frozen’ webserver.


Overal performance: these PHP-sites have become slow and unpredictable.
(As webbrowser, I used the updated versions of: Edge, Firefox and Opera.)

Do you know what could be the main cause of this FastCGI problem?
Do you know what the correct combination/implementation/settings should be, to get these websites working properly,
regarding versions of: Piwik, Piwigo, Imagick, Visual C++ Redistributable, PHP - FastCgi ?

Environment:
Piwik 3.2.0
Piwigo 2.9.2 (www.rolfsnijders.net)

Operating system: WINNT: Windows 10 prof 32bit, webserver: IIS 10
PHP: 7.1.7 [2017-11-21]
MySQL: 5.5.54

Imagick Graphics Library: External ImageMagick 7.0.5-1
Installed on webserver:
a) ImageMagick-7.0.5-1-Q16-x86-dll.exe (desktop software).
b) Relevant content of: php_imagick-3.4.3rc4-7.1-nts-vc14-x86.zip (PHP-extension).

Friendly regards,
Rolf