When you notice an issue that is same as below screenshot as shown. It means that aiToons are not supported for GPU render. The aiToon shader is working as normal.
How to use AiToon Shader without GPU supported in Arnold renderer
Solution:
1. In Render Setting, Switch the Render device from “GPU” to “CPU”.
2.Go to “Sampling” / “Filter” , and then “type” switch to “Contour”.
3. Assign aiToon Shader to an object.
4. Add a lighting.
5. Open “Arnold RenderView” to render.
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Tips and Tricks
from artist.B