I'm having a very annoying GPU rendering issue that I was wondering if anyone has any suggestions for? I'm doing some GPU renders and for some reason my iris (which is behind a transmissive cornea piece of geo) is coming out much darker than in CPU. I assumed it was a ray depth issue, but increasing the transmission and transparency depth seems to have no effect. The two look exactly the same when the glass shaded cornea ontop is removed which is what leads me to think it's something to do with GPU and transmission or transparency depth. Anyone ever had this or know what could be causing the difference? I've done loads of tests to see if it's a shader setting that is causing it as I'm using SSS but it is 100% to do with the glass shader infront of the eye as when I remove that the iris looks the same in both CPU and GPU.
I've checked every render setting, geo setting and shader setting I can think of with no luck. Unfortunately the GPU documentation for Arnold leaves much to be desired...
And no, it's nothing to do with the CPU render not being finished, I did plenty of tests where I let it run to completion that gave exactly the same discrepency.
UPDATE: I was asked if caustics were on, they were not and I've done some tests here that show that while it does help it's only putting a band-aid over the real underlying problem I've been unable to diagnose: