Canon LBP6030W: Printing still in process but no jobs queued

first, I appreciate the time you spent reading this and helping me.
What happened:
- I printed a 20-ish-pages document via wifi. Half way through the printing, my printer ran out of paper. Then, I took a look at Devices>Printers and found out there's NO active job.
'no active jobs shown'
- Meanwhile, the out of paper indicator on the printer was still flashing. Pressing it resumed the job, as I expected.
The problem:
- How can I cancel a print job that is half-way finished while there is no job listed in Devices>Printers?
My inspection:
- When I sent a print order, I did see the printer recieved the job (in Devices>Printer). But it only showed that for roughly 3 seconds before turning back to 'no active jobs'.
What I tried:
- lprm returned lprm: No active jobs on (my printer name)
- sudo service cups restart: Nothing changes.
- localhost:631/jobs shown all the jobs were finished
'all jobs completed'
My system
Thinkpad L390, dual-boot Windows 10 1909 and Ubuntu 19.10
****EDIT

Hope the following info helps

service cups status

● cups.service - CUPS Scheduler Loaded: loaded (/lib/systemd/system/cups.service; enabled; vendor preset: ena Active: active (running) since Mon 2020-03-02 11:55:00 +07; 17min ago Docs: man:cupsd(8) Main PID: 1044 (cupsd) Tasks: 5 (limit: 4915) Memory: 9.8M CGroup: / ├─1044 /usr/sbin/cupsd -l ├─1178 /usr/lib/cups/notifier/dbus dbus:// ├─1179 /usr/lib/cups/notifier/dbus dbus:// ├─1180 /usr/lib/cups/notifier/dbus dbus:// └─1181 /usr/lib/cups/notifier/dbus dbus://
Mar 02 11:55:00 Thinkpad-L390-LS systemd[1]: Started CUPS Scheduler.

ps -fu lp

ID PID PPID C STIME TTY TIME CMD
lp 1178 1044 0 11:55 ? 00:00:00 /usr/lib/cups/notifier/dbus dbus
lp 1179 1044 0 11:55 ? 00:00:00 /usr/lib/cups/notifier/dbus dbus
lp 1180 1044 0 11:55 ? 00:00:00 /usr/lib/cups/notifier/dbus dbus
lp 1181 1044 0 11:55 ? 00:00:00 /usr/lib/cups/notifier/dbus dbus

lpstat -t

scheduler is running
system default destination: Canon-LBP6030-6040-6018L
device for Canon-LBP6030-6040-6018L: socket://192.168.1.6
Canon-LBP6030-6040-6018L accepting requests since Mon 02 Mar 2020 09:18:25 +07
printer Canon-LBP6030-6040-6018L is idle. enabled since Mon 02 Mar 2020 09:18:25 +07

Content from var/log/cups/error_log as follow

E [01/Mar/2020:23:15:27 +0700] [Client 54] Returning IPP client-error-document-format-not-supported for Send-Document (ipp://localhost:631/printers/LBP6030w-6018w) from localhost.
E [01/Mar/2020:23:17:14 +0700] [Client 9] Returning IPP client-error-document-format-not-supported for Send-Document (ipp://localhost:631/printers/LBP6030w-6018w) from localhost.
W [01/Mar/2020:23:28:00 +0700] CreateProfile failed: org.freedesktop.ColorManager.AlreadyExists:profile id \'LBP6030w-6018w-Gray..\' already exists
E [01/Mar/2020:23:40:39 +0700] [Client 32] Returning IPP client-error-document-format-not-supported for Send-Document (ipp://localhost:631/printers/LBP6030w-6018w) from localhost.
W [01/Mar/2020:23:55:06 +0700] CreateProfile failed: org.freedesktop.ColorManager.AlreadyExists:profile id \'LBP6030-6040-6018L-Gray..\' already exists
E [02/Mar/2020:00:01:44 +0700] [Client 110] Returning IPP client-error-not-possible for Cancel-Job (ipp://localhost/jobs/5) from localhost.
E [02/Mar/2020:00:01:51 +0700] [Client 112] Returning IPP client-error-not-possible for Cancel-Job (ipp://localhost/jobs/4) from localhost.
W [02/Mar/2020:00:03:19 +0700] CreateProfile failed: org.freedesktop.ColorManager.AlreadyExists:profile id \'LBP6030-6040-6018L-Gray..\' already exists
E [02/Mar/2020:00:17:30 +0700] Scheduler shutting down due to program error.
E [02/Mar/2020:00:17:53 +0700] Scheduler shutting down due to program error.
X [02/Mar/2020:00:18:11 +0700] No valid Listen or Port lines were found in the configuration file.
X [02/Mar/2020:00:18:11 +0700] No valid Listen or Port lines were found in the configuration file.
X [02/Mar/2020:00:18:11 +0700] No valid Listen or Port lines were found in the configuration file.
X [02/Mar/2020:00:18:11 +0700] No valid Listen or Port lines were found in the configuration file.
X [02/Mar/2020:00:18:11 +0700] No valid Listen or Port lines were found in the configuration file.
E [02/Mar/2020:00:26:18 +0700] Scheduler shutting down due to program error.
E [02/Mar/2020:00:27:43 +0700] Scheduler shutting down due to program error.
E [02/Mar/2020:00:32:03 +0700] [Client 17] Returning IPP client-error-not-possible for Cancel-Job (ipp://localhost:631/printers/LBP6030-6040-6018L) from localhost.
E [02/Mar/2020:00:43:32 +0700] [Job 18] The printer is not responding.
E [02/Mar/2020:00:44:02 +0700] [Job 18] The printer is not responding.
E [02/Mar/2020:00:44:32 +0700] [Job 18] The printer is not responding.
E [02/Mar/2020:00:45:59 +0700] [Client 242] Request from "localhost" using invalid Host: field "[v1.::1]:631".
E [02/Mar/2020:00:45:59 +0700] [Job 16] Unable to queue job for destination "LBP6030-6040-6018L".
E [02/Mar/2020:08:34:35 +0700] [Job 16] Files have gone away.
E [02/Mar/2020:09:18:31 +0700] [Client 56] Returning IPP client-error-not-possible for Cancel-Job (ipp://localhost/jobs/20) from localhost.
E [02/Mar/2020:09:20:01 +0700] [Client 61] Returning IPP client-error-not-possible for Cancel-Job (ipp://localhost/jobs/20) from localhost.
E [02/Mar/2020:09:34:21 +0700] [Client 65] Returning IPP client-error-not-possible for Cancel-Job (ipp://localhost:631/printers/Canon-LBP6030-6040-6018L) from localhost.
E [02/Mar/2020:09:35:30 +0700] [Client 66] Returning IPP client-error-not-possible for Cancel-Job (ipp://localhost:631/printers/Canon-LBP6030-6040-6018L) from localhost.
W [02/Mar/2020:10:54:17 +0700] Notifier for subscription 181 (dbus://) went away, retrying!
W [02/Mar/2020:10:54:17 +0700] Notifier for subscription 183 (dbus://) went away, retrying!
W [02/Mar/2020:10:54:17 +0700] Notifier for subscription 187 (dbus://) went away, retrying!

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