I have the exact same problem, four out of the 10 two-color starter decks disappeared from my collection.

I'm missing 2 of my starter decks as well after the last update to Arena. Currently missing Ignite the Future (Black/Red)and Spellweaver (Blue/Red).

Same issue for me as well. I completed the color challenge previous and had access to all of the starter decks and after the update I am missing some of them.

Same here, before the recent update I had all of them and after the update I've noticed 4 preconstructed decks missing from the list and when I tried to recreate them from the cards listed in the starter decks event it turned out I am missing cards. And yes I have completed all colour challenges and the win games challenges to unlock the decks in the past.

Also missing starter decks

Same issue here. Missing Ignite the Forge and On the Hunt.

After the most recent update, four of the starter decks have disappeared from my "Decks" page under "Starter Decks".
I understand some of the starter decks have been updated with new cards, but they have not been added to my collection. None of the starter decks which do appear on the "Decks" appear to have been updated with new cards either.
I tried the "Starter Deck Duel" event to see if I could get the missing decks/cards that way. However, despite getting three wins with the "Ignite the Forge" deck, the deck was not added to the "Decks" page and I did not receive the cards added with the update such as "Junkyard Genius".

I am also having the same issue

I am missing multiple precon decks from the Color Challenge as well as many of the decks from the new Starter Deck Challenge.

I noticed in logging in that 4 of the starter decks are missing. Specifically, the RU, WB, BR, and RG decks. I did not see any way to earn them, and it said I had completed the color challenge already(which I did some time ago)

Some of my decks are missing cards that I had. Most of the single color starter decks I can't use cuz cards are missing