Some of our clients reporting errors due to a missing api-ms-win-crt-stdio-l1-1-0.dll with MSVC 2015 apps. This file is contained in the Universal C Runtime, which should be included in the Visual C++ Redistributable for Visual Studio 2015. However, these customers have to manually download and install an updated Universal C Runtime to get the applications to start.

I don't know the exact reason, but it seems like Qt's Visual C++ Redistributable for Visual Studio 2015 doesn't include all the files that are needed to run Qt apps on older (possible not up-to-date) Windows versions.

See also this quote from https://support.microsoft.com/en-us/kb/2999226

Microsoft Visual Studio 2015 creates a dependency on the Universal CRT when applications are built by using the Windows 10 Software Development Kit (SDK). You can install this update on earlier Windows operating systems to enable these applications to run correctly.

This may or not be related to QTBUG-48659, maybe they are even duplicates.