MrRaf

Hi MrRaf,
Thanks for the files. I've spent some time looking into this issue and it appears to be a common issue when the printer does the colour conversion - it can often mess with the transparency. If your printer driver offers any form of colour correction such as Intelligent Colour etc then first try disabling this. 

If that doesn't work you can use the 'Rasterise Entire Page'  option on the Printer dialog's Rasterisation section, or alternatively rasterise your page before sending it to the printer. It does seem to be a common problem in other applications as well:
https://graphicdesign.stackexchange.com/questions/64504/pdf-from-indesign-looks-correct-but-prints-bounding-boxes-around-effects-and-tra
https://helpx.adobe.com/creative-suite/kb/white-box-or-color-wash.html
https://forums.adobe.com/thread/2401513

Hey Sean P,
Forgive my delayed response, but doing a "Rasterise Entire Page" seemed to do the trick, unless it was the update that did it. Either way, this was very helpful. Thank you.