Sometimes PDFs are generating without graphics.

Dear SolidWorks,

We are programmatically converting .slddrw (drawing) file to PDF's using console application in C# by referring the documentation given by SolidWorks. We have a dedicated Machine (Windows 10 OS) to perform this job. PDFs are generating successfully without any issues but sometimes, PDFs are generating without Graphics in the drawing, if we try again, it's working as expected, If the issue persist, by restarting the System we can resolve the issue. We verified the license, and we have dedicated license as well. can you help us, what is the cause of this intermediate issue?