[cups] Problems printing two files in one job

[Claus Tøndering]

I have an HP OfficeJet Pro 6970 printer. I'm running CUPS 2.4.1 on 
Ubuntu 22.04.1 LTS.

My problem is that I cannot get CUPS to print two files as one job. I 
try to print two files from the command line thus:

     $ lp alpha.txt beta.txt

The lpq command gives this output:

     $ lpq
     HP_OfficeJet_Pro_6970_7BE7A4 is ready
     Rank    Owner   Job     File(s)                         Total Size
     1st     claus   62      alpha.txt                       2048 bytes

Here, it mentions only the file alpha.txt. However, only the file 
beta.txt is actually printed. alpha.txt is not printed.

When I use lp to print more than one file, these messages appear the 
/var/log/cups/error_log:

    W [13/Dec/2022:16:58:28 +0100] [Job 62] /tmp/126c463a5b414: file is 
damaged
    W [13/Dec/2022:16:58:28 +0100] [Job 62] /tmp/126c463a5b414 (offset 
14802): xref not found
    W [13/Dec/2022:16:58:28 +0100] [Job 62] /tmp/126c463a5b414: 
Attempting to reconstruct cross-reference table

The first digits of the filename (in this case 126c4) appear to always 
be the hexadecimal value of the PID of the gstoraster CUPS filter that 
runs as part of the printing process.

I've enabled debugging, and the resulting error log (366KB) can be 
downloaded here:
https://www.dropbox.com/s/fe7oruwlek1p1rz/lperror_log.txt?dl=0

What is the problem here, and why is only one file printed?

Until recently, I used CUPS 2.3.1 on Ubuntu 20.04 LTS. I had the same 
problem then. I did a complete reinstall of everything, but my present 
system (CUPS 2.4.1 on Ubuntu 22.04.1 LTS) still has the problem.

This is not a very big problem for me. I can always print the files as 
separate jobs, but something must be wrong nevertheless.

Thanks for any help.


/Claus