I have Visual C++ installed in VS2017. Is that the package that includes the MSVC 19.14 compiler? I remember I didn't see this compiler mentioned specifically, so I thought maybe it is missing.
In trying to verify that this particular compiler is installed I found this link which describes a compiler issue with the now included version 19.15:
https://github.com/appveyor/ci/issues/2598. Could it be related?