Crazy I just got those card and it’s missing . Who knows how many other card has disappear from my collection.
[EDIT: Ooops, I realize now why I wasn't seeing some cards, I was in the Commander Deckbuilder where it only shows one of each card. This is embarrassing, but I am admitting my mistake here in the hope that it may help others. Thanks!]
This seems to have happened to me as well, one card I know for sure was in a booster pack I opened about an hour ago that was a duplicate of a card I already had a copy of:
Not sure if that will help the devs.
For this issue, please submit at: https://mtgarena-support.wizards.com/hc/en-us/requests/new and select 'General Questions'.