Black radial wipe in Media Encoder, even with white solid background

Impossible to understand your problem without any actual screenshots. From layer styles to blending mottes/ matte modes there could be anything at play. And ultimately it becomes the question why you would even apply a wipe to an adjustment layer of all things, when it's generally better to pre-compose and apply it as a whole.

Mylenium

Update: solved the problem, though I am still curious as to why it works this way.

Turns out I had the radial wipe adjustment layer placed on top of a layer with a looping texture overlay. When I moved the wipe below the texture it rendered without the black.

Hope this helps somebody. And if anyone knows why this happens I'd be curious to know. Cheers 🙂