Nexon promised their players on November 14, 2018 in Game Update v.200 that they would stop removing Medals from player's collections when events that gave medals were reinstated.
This promise was broken on Wednesday, January 24, 2019 as Game Update v.202 became live.
This picture details where the Chocophile medal was and also notes my current, decreased, medal count.
Point A] Represents where the Chocophile medal was before Nexon deleted it.
Point B] Represents my current medal count. It used to be 318 prior to Game Update v.202.
Point C] Represents the name of the 'Clairvoyant' medal. I have my medal window sorted alphabetically in the picture, so again, referring to 'Point A', the Chocophile once lay immediately left.
What Nexon has done was both fall back on their word and also force players who had already earned the Chocophile medal from the 'Choco Onslaught' content that will be reinstated at 'UTC: February 13 at 12:00 AM – March 5 at 11:59 PM' to perform double work at obtaining a medal that was rightly theirs the first time around.