So, just an update. After getting in touch with Stefano, it was determined that the "Surface Force" node in my tree was spitting out invalid point IDs. My emitter geo was sitting pretty much right on top of the geo I was plugging into that node, so I just gave the emitter geo a slight push as a simple workaround for now.
Here's Stefano's response as well:
"Arnold fails because there is at least one strand point position with
Nan coordinates, caused by the Add Force node in your compound. We
don't do any particular check on the coordinates before sending them to
Arnold. It's Softimage that returns the invalid values to the exporter. The first invalid strand is #10. If you emit 10 strands, you should see the render working. If you raise to 11, it fails, because of strand #10. If you display the points id in the viewport, you'll see no #10 (with 15, also #13 is gone, as showing below).
So, I guess that the display skips #10 because invalid, yet it's sent to the exporter by the sdk. If you manage to get rid of these invalid cases, it should work again. It's probably the Surface Force node that pushes out some invalid vector in the first place.
Let me know. Ciao. Stefano"