This issue is directly related to this one https://feedback.filerun.com/en/communities/1/topics/592-iis-500-internal-server-error-when-enable-imagemagick-or-ffmpeg
I have this problem for years since the first installation on IIS server, but I didn't know it is related to FFMpeg and GraphicsMagick. I thought it is related just to FastCGI protocol setting.
FastCGI on IIS server has protocol settings:
When protocol is set to NamedPipe this issue with error 500 always occurs time to time (usually after listing a few pages with files that use FFMpeg or GraphicsMagick for image previews).
In case of setting protocol to Tcp - no more Error 500 related to FFMpeg and GraphicsMagick being turned on. At the same time another issue (even more severe) appears. While downloading big files it suddenly interrupts and I can see Error 500 in the webserver logs and it happens all the time after downloading a few GB (no issues on uploading). When NamedPipe is used then I can download hundreds GB without any issues.
I tried to change different FastCGI settings and other webserver settings, but nothing works.
Customer support service by UserEcho