What causes discoloration on a 2021 Ford Expedition door handle?

Answer 1: It’s best to pull the sweep and pop those panels off before install. They can be ruined quite easily. 

Answer 2: If water permeates the cardboard backing behind the leather, the panels are pretty much ruined. This is caused by water going through the holes in the stitching, which causes the backing to expand. There may also be vinyl backing. Either way, enough water permeation will ruin the panel.