Since re-installing from OpenSUSE 42.1 to 42.3, KDE (QT5) apps such as Okular,
Konsole, Kate, and even assistant-qt5 are unable to print to remote printers
(served via a CUPS print server).  The GUI will not throw any exceptions. 
However, Okular will print the following to the console (if started that way):

lpr: The printer or class does not exist.

In another case, it printed to the first printer in the list rather than the
one selected.  Note that we have 149 printers defined (as shown in lpstat -t). 
Perhaps the long list of printers is causing some sort of overflow ?

Note that other software such as firefox is printing fine from the same user
session.

Here is what is printed on the console with QT logging enabled:
$ QT_LOGGING_RULES=org.kde.okular.core=true okular            
org.kde.okular.core: Executing "lpr" with arguments ("-P", "", "-#1", "-J",
"Dell.pdf", "-r", "/tmp/okular_S21220.ps")
lpr: The printer or class does not exist.

Bug opened with KDE Okular developers.  They confirmed it is an upstream bug.
Bugzilla opened with KDE: https://bugs.kde.org/show_bug.cgi?id=383139

They also referenced another distro that had the same type of bug which was
fixed by rebuilding cups-filters against another version of libqpdf:
http://advisories.mageia.org/MGAA-2017-0055.html