I had discussed this with the StirlingPDF dev here: Some PDF's PDF-to-Img but others fail · Stirling-Tools/Stirling-PDF · Discussion #2784 · GitHub
We couldn’t quite get to the bottom of it.
Basically, when n8n sends a PDF to StirlingPDF if the parameter “singleOrMultiple” is “single”, it works fine.
If instead we change it to “multiple” (split the file into multiple images and zip it), something goes wrong in SterlingPDF.
However, if I use curl to run the same request as n8n, it works fine.
Really strange.
The thing is, it doesn’t happen for all files either.