OK, I have a sample document to share now. I've pulled out one page from a document exhibiting this error that does not have any identifying information on it.
I noticed in the process of doing this, that the same original document (they usually come in as PDFs) split into TIFFs by other applications (i.e., FoxIt) don't seem to run into issues. The TIFFs are not invalid when I look at them on my personal PC. However when the document goes through our pipeline and is split into TIFFs in preparation for being OCR'd, Tesseract throws the "defaultPdfEncoding" error mentioned above. Unfortunately unless I know exactly what about this document is causing this, I won't be able to address it in our pipeline.