A bit confused about "Quality Issues" rejections for my simple line art illustrations

Hi everyone,

I’m a bit stuck and was hoping to get some advice from the community.

I recently uploaded some high-resolution PNG illustrations (8000x8000 px) created in Clip Studio Paint. However, they keep getting rejected for "Quality Issues" citing noise or artifacts.

I'm a bit confused because I used an oil-paint style brush to give the lines some character, so there's intentional texture in the art. I’ve even tried uploading files where the edges are absolutely smooth and only the filled areas have textures, but the rejection reason remained exactly the same.

I know as a raster file, it won't have the perfectly smooth edges of a vector, but I see a lot of other textured art on Adobe Stock. Is the system misidentifying hand-drawn textures as technical flaws? Or should I be prepping my files differently?

Also, since these are just simple line art character sketches without any color fills, would it be better to just upload them as JPGs instead of PNGs? I’m wondering if the transparency might be causing the noise filter to trigger.

I'd really appreciate any tips or experiences you guys could share. Thanks a lot!