Could the red color in solution be a polysulfide? The ICP results show >10% sulfur, and polysulfides in solution have that same rich orange-red color. See, for example, NileRed dissolving sulfur, making an (alkaline) polysulfide solution:
If the red color is polysulfides, then the precipitate could just be sulfur, which crystallizes out of some polysulfide solutions.
This is 100% theory. Has anybody dissolved pyrites in aqua regia and gotten a similar result?
If you got that by premixing HCl and HNO3, you should spend some time studying the forum. We advise against premixing AR. You are better off adding the HCl you feel you will need / enough to cover your feedstock, then adding the nitric in increments.