CUPS - lp doesn't print when given more than one file

I have a Brother HLL2390DW all in one connected by USB to my Kubuntu 22.04 notebook using brother-HLL2390DW-cups-en.ppd from their website.

If I issue an lp file1.pdf it works fine, but if I issue an lp file1.pdf file2.pdf, the printer wakes up, but doesn't print anything.

/var/log/cups/error_log shows

W [23/Nov/2024:00:00:28 -0500] Printer drivers are deprecated and will stop working in a future version of CUPS. See https://github.com/OpenPrinting/cups/issues/103W [23/Nov/2024:02:05:49 -0500] Printer drivers are deprecated and will stop working in a future version of CUPS. See https://github.com/OpenPrinting/cups/issues/103W [23/Nov/2024:05:17:30 -0500] Printer drivers are deprecated and will stop working in a future version of CUPS. See https://github.com/OpenPrinting/cups/issues/103E [23/Nov/2024:18:22:58 -0500] [Job 66] Unable to add document to print job.E [23/Nov/2024:18:46:36 -0500] [Job 67] Unable to add document to print job.E [23/Nov/2024:18:59:48 -0500] [Job 69] Print job canceled at printer.W [23/Nov/2024:18:59:48 -0500] [Job 69] Backend returned status 5 (cancel job)E [23/Nov/2024:19:04:23 -0500] [Job 70] Unable to add document to print job.E [23/Nov/2024:19:04:31 -0500] [Job 70] Print job canceled at printer.W [23/Nov/2024:19:04:31 -0500] [Job 70] Backend returned status 5 (cancel job)

$ lpstat -aBrother_HL_L2390DW_USB not accepting requests since Sat 23 Nov 2024 05:36:03 PM EST -        Rejecting JobsBrotherHLL2390D not accepting requests since Sat 02 Nov 2024 08:10:19 PM EDT -        Rejecting JobsHLL2390DW accepting requests since Sat 23 Nov 2024 07:12:01 PM EST

The other two instances were from previous attempts to hook up the printer as a networked printer using an Ethernet to USB print server adapter, etc. (I'll ask a separate question about that once this works.) I manually disabled them.