All Invoice PDFs are Corrupt

[smartinec]

$dataService->DownloadPDF($invoice) results in a corrupt PDF file. The files are 15KB and appear to be fine, but appear blank in Chrome/Safari and MacOS preview says the file is damaged and won't open. I can provide sample files privately. Here is first few and last few lines:

%PDF-1.7
4 0 obj
<</Type /Page/Parent 3 0 R/Contents 5 0 R/MediaBox [0 0 612 792]/Resources<</Font<</FAAAAH 7 0 R/FAAAAJ 9 0 R/FAAABC 12 0 R>>/XObject<</X1 14 0 R>>>>/Group <</Type/Group/S/Transparency/CS/DeviceRGB>>>>
endobj
5 0 obj
<</Length 15 0 R/Filter /FlateDecode>>stream
...
endstream
endobj
startxref
15102
%%EOF