Bugzilla

Just in case this crops up again, I'll preserve one possible insight:

Our working theory (before the bug stopped reproducing for Martin) was that it might have something to do with the fact that the print-job-name shown in the print queue is extremely long -- it seemed to include the full data URI, which was 200,084 characters long.  (The UI shows it with an ellipsis, but it was at the window boundary which suggests that it's the print-queue UI that's doing that ellipsizing.)

When printing just the PDF file directly (which always worked for Martin), the print queue showed the PDF filename instead (as you'd expect).
And when printing from Edge (which also worked for Martin), the print queue showed a truncated version of the data URI.

So it's conceivable that a flaky print driver, or some other intermediate print-related mechanism, was getting confused by the extremely-long "job title" (or whatever the appropriate name would be).  If that were the case, then we could take some actions on our side to truncate that title at some reasonable upper limit, to avoid tripping this driver bug (or whatever it is).  But without the ability to reproduce the issue anymore, it's not worth pursuing that at this point.

Just in case this crops up again, I'll preserve one possible insight:

Our working theory (before the bug stopped reproducing for Martin) was that it might have something to do with the fact that the print-job-name shown in the print queue is extremely long -- it seemed to include the full data URI, which was 200,084 characters long.  (The UI shows it with an ellipsis, but it was at the window boundary which suggests that it's the print-queue UI that's doing that ellipsizing and that the internal representation of that print-job-title might really have the full data URI.)

When printing just the PDF file directly (which always worked for Martin), the print queue showed the PDF filename instead (as you'd expect).
And when printing from Edge (which also worked for Martin), the print queue showed a truncated version of the data URI.

So it's conceivable that a flaky print driver, or some other intermediate print-related mechanism, was getting confused by the extremely-long "job title" (or whatever the appropriate name would be).  If that were the case, then we could take some actions on our side to truncate that title at some reasonable upper limit, to avoid tripping this driver bug (or whatever it is).  But without the ability to reproduce the issue anymore, it's not worth pursuing that at this point.