Starting scenario:
- VM cupstest1 "Print server":
  1. Installed with openSUSE 15.3-2 Net ISO and server role
  2. Firewall stopped and disabled
  3. cupsd.conf:
     - LogLevel debug
     - Listen *:631
     - All <Limit> blocks: Allow from all
     - DefaultPolicy allowallforanybody
  4. systemctl restart cups
  5. Installed cups-pdf RPM
  6. Added new printer via the CUPS Web interface:
     - Local printer -> CUPS-PDF (Virtual PDF Printer)
     - Name: "vpdf"
     - Description: "Virtual PDF Printer" (default value)
     - Share printer in network: enabled
     - Manufacturer: "Generic"
     - Model: "Generic CUPS-PDF Printer (no options)"
  7. Test new printer locally on cupstest1 with "lpr -Pvpdf /etc/shells"
     --> /var/spool/cups-pdf/root/shells__l_cups-pdf_root.pdf created correctly
  8. VM snapshot
- VM cupstest2 "Print client":
  1. Installed with openSUSE 15.3-2 Net ISO and xfce desktop role
  2. Firewall stopped and disabled, SSH started and enabled
  3. /etc/hosts entry for cupstest1 with IP address made
  4. cupsd.conf:
     - LogLevel debug
     - Listen *:631
     - All <Limit> blocks: Allow from all
     - DefaultPolicy allowallforanybody
  5. systemctl restart cups
  6. Tested direct printing with "lpr -Hcupstest1 -Pvpdf /etc/shells"
     --> /var/spool/cups-pdf/ANONYMOUS/shells__0.pdf created correctly on cupstest1
  7. VM snapshot

Then:
- On cupstest1:
  1. Install "avahi" RPM (not installed in default server role)
  2. systemctl restart cups
- On cupstest2:
  1. Install "avahi-utils"
  2. "avahi-browse -akr" shows mDNS records for "Virtual PDF Printer @ cupstest1._ipps._tcp.local" (and _ipp and _printer) are received
  3. "lpstat -t" confirms no CUPS queues so far as cups-browsed is not running
  4. "systemctl start cups-browsed"
  5. "lpstat -t" shows new "Virtual_PDF_Printer_cupstest1" queue.
  6. Test printing with "lpr -PVirtual_PDF_Printer_cupstest1 /etc/shells"
     --> no new file in /var/spool/cups-pdf/ANONYMOUS on cupstest1!

cupstest1 /var/log/cups/error_log only shows "Get-Printer-Attributes" request.

cupstest2 /var/log/cups/error_log shows:
1. [Client 17] Get-Printer-Attributes request
2. [Client 17] CUPS-Get-Printers request
3. [Client 17] CUPS-Get-Default request
4. [Client 17] Get-Printer-Attributes request
5. [Client 17] Create-Job request -> Job 1
6. [Client 17] Send-Document request
7. Job 1 with "3 filters for job:"
   1. "texttopdf (text/plain to application/pdf, cost 32)"
   2. "- (application/pdf to printer/Virtual_PDF_Printer_cupstest1/application/pdf, cost 0)"
   3. "- (printer/Virtual_PDF_Printer_cupstest1/application/pdf to printer/Virtual_PDF_Printer_cupstest1, cost 0)"
5. texttopdf filter and implicitclass backend started
6. [Client 17] Closing connection
7. [Client 13] CUPS-Add-Modify-Printer request as "" -> 401
8. [Client 18] Broken pipe
9. [Client 19] Broken pipe
10. [Client 20] CUPS-Add-Modify-Printer request as "root" --> sets cups-browsed-dest-printer-default
11. [Client 20] CUPS-Get-Printers request
12. [Client 20] CUPS-Get-Printer-Attributes request ipp://localhost:631/printers/Virtual_PDF_Printer_cupstest1
13. [Client 21] CUPS-Get-Printer-Attributes request ipp://localhost:631/printers/Virtual_PDF_Printer_cupstest1
14. Job 1 receives destination URI ipps://cupstest1.local:631/printers/vpdf
15. [Job 1] gziptoany started
16. texttopdf exited with no errors
17. gziptoany exited with no errors
18. [Job 1] Started IPP backend
19. [Job 1] The IPP backend exited with the status 0
20. [Client 21] Broken pipe
21. implicitclass exited with no errors
22. [Job 1] Job completed
23. [Client 22] Get-Jobs request
24. [Client 22] Broken pipe
25. [Job 1] Unloading

/var/spool/cups/c00001 and d00001-001 still exist.

Then:
1. In /etc/cups/cups-browsed.conf set "LogDir" and "DebugLogging file"
2. /var/log/cups/cups-browsed_log shows nothing strange
3. Test printing again with "lpr -PVirtual_PDF_Printer_cupstest1 /etc/shells"

/var/log/cups/cups-browsed_log now shows:
1. "[CUPS Notification] Virtual_PDF_Printer_cupstest1 is using the "implicitclass" CUPS backend, so let us search for a destination for this job."
2. "Checking state of remote printer vpdf on host cupstest1.local, IP (null), port 631."
3. "Printer vpdf on host cupstest1.local, port 631 is accepting jobs."
4. "Printer vpdf on host cupstest1.local, port 631 is idle, take this as destination and stop searching."
5. "Destination for job 2 to Virtual_PDF_Printer_cupstest1: cupstest1.local:631, queue vpdf"
6. on_printer_modified() triggers -> "Settings of printer Virtual_PDF_Printer_cupstest1 got modified, doing backup."
7. on_printer_state_changed() triggers 3 times, 2x "changed", 1x "changed to idle"
<nothing else>

/var/log/cups/error_log looks pretty much the same as described.