Iray Rendering One Color at Low Resolution

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I've been using DAZ with 3Delight for years but have just started using Iray after getting a new computer. I've tried converting and rendering one of my character models only to run into a really odd error. The purple parts of my base texture - and ONLY the purple parts - are being rendered at a very low resolution.

You can see the green bits are rendering fine, and even the bump map, which is the exact same resolution, but obviously greyscale, is also rendering fine even on the same shape. I never had this issue using the same texture file in 3Delight. I also tried converting the texture from PNG to JPEG, which didn't solve the problem. Anyone have some idea what's going on and how to fix it?