I know my reply is too late, but... I have the same problem for about 2 - 3 years. It worked many years before and the sources of pnm2ppa didn't changed. I think it can be a problem with some updated dependencies (maybe ghostscript?) I haven't figured out the exact conditions under which this happens, nor how to workaround it.
Moin, I can print on my 710c with pnm2ppa running under Ubuntu Raspberry Pi. It starts correctly but ends most printouts before the last line. When more than 1 page is printed it goes correctly through all pages until reaching the last one. Then it stops before the last line or so and the green diode blinks. Sometimes this phenomenon does not happen: I allach a file (file ..cn23) that shows this phenomenon. Thank you for help