Importing pro file creates a broken project

Any project I import with the latest Qt VS extension fails. 

mocing cpp files fail with "Could not create output file"

running uic fails with "error 1: uic (C:\Qt\5.12.3\msvc2017\bin\uic.exe)"

for some of my projects Convert custom build steps to Qt/MsBuild that runs automatically fails, popping up a dialog that simply says "illegal characters in path"

I'd provide a specific example, but literally nothing works, so there doesn't seem much point. I first experienced this today, the previous version worked without issue.