All of a sudden my HP LaserJet 2550L decided to stop printing... any idea what could be wrong?

I have an HP LaserJet 2550L. It works just fine, I could print my invoices without a problem.

The other day, I printed a different document with many lines and borders and images. While that job was going I sent a few more pages for printing and from that time on, the printer "prints white pages" only.

As far as the computer is concerned, everything looks like it printed 100% successfully. The pages of paper do go through and the printer at least pretends it's doing work, but once the pages come out, their are 100% white. Not even a little mark of black or some other color.

I recently replaced the drum and don't print much so it still functional. It's only since I printed those two things together that it seems to misbehave.

Here is the output of the lpstat command:

monster $ lpstat -l -p
printer hp-color-LaserJet-2550-series is idle.  enabled since Sun 01 Mar 2020 02:50:28 PM PST
    Form mounted:
    Content types: any
    Printer types: unknown
    Description: Hewlett-Packard hp color LaserJet 2550 series
    Alerts: none
    Location: monster
    Connection: direct
    Interface: /etc/cups/ppd/hp-color-LaserJet-2550-series.ppd
    On fault: no alert
    After fault: continue
    Users allowed:
        (all)
    Forms allowed:
        (none)
    Banner required
    Charset sets:
        (none)
    Default pitch:
    Default page size:
    Default port settings:

I'm part of the lp and lpadmin groups, although since the printing was working before, I really don't see why that would have any bearing on the matter.

Just in case, I tried to change settings many times. I turned the printer ON and OFF. I tried with 18.04 and 16.04. I tried to remove the printer and re-install it. Still plain white pages coming out on the other side. No errors reported on the computer or the printer. I tested from LibreOffice, evince, The Gimp. Same results each time. The jobs are all under 100Kb of data.

Here is a screenshot showing the many job attempts I've made. Only the "Clean Heads" failed, although I have no clue what that is and whether it is expected to fail. In any even, the printer was working before. What would make it think it should stop working in this way?!