I attach the error_log file with debug logging mode. The CUPS notifier closes after a while. That might be the problem. When I open the KDE printer dialog, the D-BUS system bus dumps these messages calling the Notifier method. Opening the printing dialog from LibreOffice writer does not print anything, not even in the session bus:

method call time=1520971612.523540 sender=:1.364 -> destination=org.freedesktop.DBus serial=1 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=Hello
method return time=1520971612.523567 sender=org.freedesktop.DBus -> destination=:1.364 serial=1 reply_serial=1
   string ":1.364"
signal time=1520971612.523580 sender=org.freedesktop.DBus -> destination=(null destination) serial=19 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameOwnerChanged
   string ":1.364"
   string ""
   string ":1.364"
signal time=1520971612.523598 sender=org.freedesktop.DBus -> destination=:1.364 serial=2 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameAcquired
   string ":1.364"
method call time=1520971612.524056 sender=:1.364 -> destination=org.freedesktop.DBus serial=2 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='ServerStarted'"
method call time=1520971612.524213 sender=:1.364 -> destination=org.freedesktop.DBus serial=3 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='ServerStopped'"
method call time=1520971612.524295 sender=:1.364 -> destination=org.freedesktop.DBus serial=4 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='ServerRestarted'"
method call time=1520971612.524399 sender=:1.364 -> destination=org.freedesktop.DBus serial=5 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='ServerAudit'"
method call time=1520971612.524514 sender=:1.364 -> destination=org.freedesktop.DBus serial=6 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='PrinterAdded'"
method call time=1520971612.524595 sender=:1.364 -> destination=org.freedesktop.DBus serial=7 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='PrinterModified'"
method call time=1520971612.524690 sender=:1.364 -> destination=org.freedesktop.DBus serial=8 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='PrinterDeleted'"
method call time=1520971612.524760 sender=:1.364 -> destination=org.freedesktop.DBus serial=9 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='PrinterStateChanged'"
method call time=1520971612.524814 sender=:1.364 -> destination=org.freedesktop.DBus serial=10 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='PrinterStopped'"
method call time=1520971612.524876 sender=:1.364 -> destination=org.freedesktop.DBus serial=11 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='PrinterShutdown'"
method call time=1520971612.524922 sender=:1.364 -> destination=org.freedesktop.DBus serial=12 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='PrinterRestarted'"
method call time=1520971612.524986 sender=:1.364 -> destination=org.freedesktop.DBus serial=13 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='PrinterMediaChanged'"
method call time=1520971612.525034 sender=:1.364 -> destination=org.freedesktop.DBus serial=14 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='JobState'"
method call time=1520971612.525087 sender=:1.364 -> destination=org.freedesktop.DBus serial=15 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='JobCreated'"
method call time=1520971612.525138 sender=:1.364 -> destination=org.freedesktop.DBus serial=16 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='JobStopped'"
method call time=1520971612.525191 sender=:1.364 -> destination=org.freedesktop.DBus serial=17 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='JobConfigChanged'"
method call time=1520971612.525238 sender=:1.364 -> destination=org.freedesktop.DBus serial=18 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='JobProgress'"
method call time=1520971612.525326 sender=:1.364 -> destination=org.freedesktop.DBus serial=19 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/org/cups/cupsd/Notifier',interface='org.cups.cupsd.Notifier',member='JobCompleted'"
method call time=1520971612.525379 sender=:1.364 -> destination=org.freedesktop.DBus serial=20 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/com/redhat/PrinterSpooler',interface='com.redhat.PrinterSpooler',member='PrinterAdded'"
method call time=1520971612.525432 sender=:1.364 -> destination=org.freedesktop.DBus serial=21 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/com/redhat/PrinterSpooler',interface='com.redhat.PrinterSpooler',member='QueueChanged'"
method call time=1520971612.525484 sender=:1.364 -> destination=org.freedesktop.DBus serial=22 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/com/redhat/PrinterSpooler',interface='com.redhat.PrinterSpooler',member='PrinterRemoved'"
method call time=1520971612.525541 sender=:1.364 -> destination=org.freedesktop.DBus serial=23 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/com/redhat/PrinterSpooler',interface='com.redhat.PrinterSpooler',member='JobQueuedLocal'"
method call time=1520971612.525592 sender=:1.364 -> destination=org.freedesktop.DBus serial=24 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
   string "type='signal',path='/com/redhat/PrinterSpooler',interface='com.redhat.PrinterSpooler',member='JobStartedLocal'"