I have tested the scenario and have managed to reproduce the problem that conversion of your PDF document to PDFA causes exception. For the sake of correction, I have logged it as PDFNET-42181 in our issue tracking system.
Please be patient and spare us little time for investigation. We are sorry for this inconvenience.
Would you be so kind to provide us with status on the PDFNET-42181 issue?
We are afraid that earlier logged issue could not get resolved due to other high priority issues in the queue. We will surely inform you as soon as there are some certain updates regarding its resolution. Please spare us little time.
We are sorry for the inconvenience.