I dont see any “platform bug report” category on the devforum, so I’ll choose platform usage support instead.
As seen above, you can replicate it by creating an image label, set ScaleType to Slice, and then define the slices, then add a UI corner as a child of the image label.
Now, I know a way to fix it (using a canvasgroup) but there is no harm in reporting it to the devs.