Using the difference between World position and World position excluding material offsets for the opacity mask creates black areas.

Development Rendering
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5

What… I have the exact same setup and my result is completely different

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FIrst: my object is semi-transparent in the preview and completely transparent in game.

Then if I invert the 0 and 1 I get the error again:

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(The grey areas in the preview are where it shows the black area in game)