I can think of two possible reasons why you might have not been able to print the boarding passes.
The first being that a pop-up window was being blocked from opening. Quite often you have to click on the yellow bar that will appear under the menu bar and click on temporarily allow pop-ups, in order for the print command to work.
If the boarding pass was formatted as a pdf file you have to click on the print button inside the pdf window, very frequently you can't print using the "print button" under "File" when trying to print a pdf image. --- Karen H.