This definitely needs an answer.
In fact, until OP can give us the right answer, we immediately need even wrong answers!
You reading this. Yes, you. Give your best wrong answer below.
In fact, until OP can give us the right answer, we immediately need even wrong answers!
You reading this. Yes, you. Give your best wrong answer below.
Input looked fine and invoking each step manually worked fine as well.
Come to find out that certain PDFs contained color calibration information that, combined with how we were calling it, would treat ARGB as RGB. The input would have transparency info defined and the thumbnail generator would happily repurpose the alpha channel as the red channel instead.