It seems to work consistently if I just run the setup file as is, I even removed a completion message, which I thought might have a wild shot at being the explanation (cannot find files if no completion message, all files found if completion message shows).

However, adding the /Q switch makes things unreliable, and not sure I really need to, considering that I have no prompt and no license. I am also not getting the prompt to reboot anymore, but I wonder if that has to do with me repeatedly installing the package to test.