On the 25th of December (and onward), when gifting cosmetics, the list allows gifting duplicate cosmetics (See screenshots for example). Prior to the issue, the gifting box would remove players’ names from the list of players you could gift a cosmetic to if they already had the cosmetic.
This was in the NA Hub, on Switch / Android / iOS
[images are in chronological order, from selecting the cosmetic (endolotl pet), to the player list. These are from my friend who plays on switch. Last photo is my endolotl pet, which I obtained about a year ago.]
(Issue similar to that of “ Got gifted something I own ” except it wasn’t a random gift. Both friends of mine who figured this out with me gifted a bunch of things that I obtained months prior 
)