Victory. 😄
The problem was Linux’s automatically discovered, driverless IPP queue—not the printer, network, or CUPS itself. The permanent HP_M402n_Direct queue bypasses that faulty raster conversion and is now your default printer.
Your ordinary documents should print normally now. The stranded old jobs will remain queued, so clear only those failed jobs with:
cancel -a HP_LaserJet_M402n_1272CA
The new direct queue and successful test print remain untouched. On the second Linux machine, we can create the same direct queue using the same IP address and PostScript driver.