So, I got reported a problem with my already released character set.

Here's the Superfly version of her skin shader (External outputs plugged to Cycles root, External inputs plugged to diffuse, bump and spec maps):

I've been testing her always with Branched Path Tracing off and Progressive Refinement on, as that works best for me and I thought the only difference in those were render times and quality in specific things. However, a customer of mine uses Branched Path Tracing on. Here's my trouble.

Branched Path Tracing off:

Branched Path Tracing on:

The only difference I could get was if I turn Volume Samples higher:

What gives? Is there anything I can tell my customer to do without me having to change her shaders (as this is an already released product)?

Answered in the Smith Micro forum. Thanks!

AS a courtesy, could you relay the answer here for those following this thread?

Sure! The Scatter Volume node shouldn't be there - I used it because I'd seen a skin shader with it from years ago, and started adding more nodes to get the look I wanted. Turns out the node wasn't even being rendered with Branched Path Tracing off to begin with, for some reason - so the rest of the shader was responsible for the entire look I wanted, and the Scatter Volume was causing all that weird redness/blackness with Branched Path Tracing. I just deleted that node and everything worked.

More details, and some tips for the SubsurfaceScattering node, on the thread I was given this answer: https://forum.smithmicro.com/topic/9665/cycles-sss-skin-and-branched-path-tracing/14