There are some times converting PDF to PDFA fails, and you have mentioned there are some bugs in the application. E.g. https://www.aspose.com/community/forums/816964/pdfa-conversion-fails/showthread.aspx#816964
Is there any library you provide that can identify that the generated document is not PDF/A compliant and we can warn the end-user appropriately? The user can then take a remedial measure.
You seem to have a library that can validate a PDFA document, but I do not know if it validates the issue if your library failed the conversion.