Installer does not launch or fails silently

I wish I had more information to provide.

• Using MUI2 and FileFunc
• RequestExecutionLevel admin
• ManifestSupportedOS Win10
• When double clicking the executable the end-user sees nothing. As if they never clicked it
• Setup is not hanging; it exits promptly as it starts.
• Function .onInit contains only SectionSetSize statements
• It only happens on ~10-20% of machines
• Executing the installer from an elevated command prompt works 100% of the time
• All machines are some flavor of Windows 10
• All users are administrators
• Setup executable and all contained executables are signed with a SHA1 and SHA256 certificate
• This seems to occur specifically on machines that have been out in the field for quite some time *

* I think it's important to mention this as help desk technicians over the past 3 years may have changed Windows settings, anti-virus may have been changed, etc.

- Just to clarify, they are double clicking the file in Explorer and they don't get a UAC dialog?

- Does UAC elevation work for other 3rd-party apps in Explorer on the problematic machines? I believe there is a UAC "silent deny non-Windows apps" policy setting.

- Why "ManifestSupportedOS Win10"? Just leave the default.

- "Setup is not hanging; it exits promptly as it starts" what does this mean? Are you seeing a process in Task manager? It is Windows that displays the UAC dialog, no process should be created before the elevation happens.