Both x86 and x64 MSVC redist dlls are missing.
This means that on a clean install of Windows 10 for example, importing shiboken2 or PySide2 will fail.
5.12.1 packages were fine in this respect.
My suspicion is that the environment variable we use to test if we run in Coin (and thus need to package dlls) has changed. Grep for "QTEST_ENVIRONMENT" in build_scripts/platforms/windows_deskop.py