In my experience, this issue is isolated only to one experience that I have made today to test something. I was going through my usual routine of creating a frame, adding a border, etc. But when I went to add an UI Corner, the engine simply ignored it, displaying it’s default square corners.
The expected result would be outlined in the following screenshot (I apologize in advance for my artistic ability):
Here is the experience in which the bug is affecting:
Copying is turned on
Edit:
I’d like to add that the UI Corner does work on buttons, but not on frames.