Me and a colleague of mine cannot print directly to our printers. If we want to print Mathematica offers only "Print to file (PDF)" but not the printers that are available to other applications. We are both running systems based on Ubuntu 16.04 x64 which uses CUPS 2.1 and Qt 5.5.
Any tips how to debug this? Or is it a known problem?
If you contact support they should be able to provide a solution. In the meantime, the best workaround is probably to save the notebook as a PDF, and print that PDF.
Followed your advice (thanks for the link) and got a reply today: Wolfram Support sent me a file libcupsprintersupport.so that we needed to place into SystemFiles/Libraries/Linux-x86-64/Qt-Plugins/printsupport. That fixed it, and printers are shown as intended.