A couple weeks ago(first noticed on 1/28), the alternate art version of Avatar - Momir Vig, Simic Visionary randomly became illegal in Freeform Vanguard. The original art version still works, but if you have the alternate art version, it shows as not a valid card in the deck and you can't play Freeform Vanguard matches with it for some reason.
Steps to reproduce:
-Build a Freeform Vanguard deck with 60 basic lands and an alternate art(#61a) Avatar - Momir Vig, Simic Visionary
-Note that the avatar incorrectly appears striped out as invalid in the deck
-Attempt to start a Freeform Vanguard match, and note that the deck incorrectly cannot be selected
-Replace the alternate art avatar with an original art one(#61), and note that it correctly appears as valid and can be used to start a match
Steps to reproduce:
-Build a Freeform Vanguard deck with 60 basic lands and an alternate art(#61a) Avatar - Momir Vig, Simic Visionary
-Note that the avatar incorrectly appears striped out as invalid in the deck
-Attempt to start a Freeform Vanguard match, and note that the deck incorrectly cannot be selected
-Replace the alternate art avatar with an original art one(#61), and note that it correctly appears as valid and can be used to start a match