Problem when importing to Spark after exporting from Lightroom

[#1]

I posted a screenshot of a collage I tried making using Adobe Spark. I also posted a screenshot of the image when opening normally on my computer. I edited the photos in Lightroom Classic and export as JPEGs (300 PPI 100 quality) and uploaded to Spark. The images look great when viewed as their own file but in a collage they get a banding to them.

[#2]

I posted a screenshot of a collage I tried making using Adobe Spark. I also posted a screenshot of the image when opening normally on my computer. I edited the photos in Lightroom Classic and export as JPEGs (300 PPI 100 quality) and uploaded to Spark. The images look great when viewed as their own file but in a collage they get a banding to them.