For those who are curious, this is what a pop up blocker does and what the problem was:
A popup blocker is a security feature built into a browser and ensures that a web page can not just open new windows or tabs without the user asking for it.
The new print option came into effect last month. The print was automatically opened as soon as it was ready. Convenient, because then you could immediately enjoy the fantastic new printing possibilities.
Because there is a short delay between clicking the download button and opening the print, your browser does not know that one is the result of the other, and so the popup blocker comes into action.
With most browsers you will see a warning that you can click on to give permission. And then there is no problem. But some users don't notice that. Or with some browsers the warning is very subtle and minimalistic, so some users just kept waiting for a result that was suppressed...
As soon as the print (PDF or image) is ready, you will now receive a clear message with a download button.
You click on that button.
Because you clicked on that button, your popup blocker does not come into action and you receive the file.