As the title suggests, the package Korblox Lord of Death’s Cape (Specifically this) has a massive quality downgrade in r6. Image 1 (Top) is r6, image 2 (bottom) is r15. Both screenshots were taken within the avatar editor, however this bug can be seen in game.
This actually isn’t the case, R6 accessories are generally downsized; it just happens to be more noticeable with certain UV mappings afaik. Related explanation: