Non-Format cards in historic when playing against friends and sparky but they work fine if I play public Historic. After looking into it, it involves specific alchemy cards but not all alchemy cards are affected. I had something similar happen some time ago and eventually they reverted back to being fine. But now the bugs back and has continued for the last couple months. I can make them work by changing my decks to direct game format but this is around twenty decks. Changing them back and forth isn't practical nor do I have the space in my deck count to just clone them all.

Bump and does anyone know how to find the cards that are throwing the error?

What happened to the red outline that showed invalid cards (in this case not actually invalid just bugged most likely)?? It is not Command Tower anymore since i have that in most His Brawl decks and they are fine. I suspect some Alchemy card appeared and has broken our decks but would love to know what is is.

edit: i figured it out by exporting the entire deck and reimporting it and saving it and comparing the decklists.

In my case it was 'Raiyuu, Storm's Edge' which inexplicably got an Alchemy card and became a 4/4 instead of a 3/3 (because apparently nobody played it and knew how powerful it was as a 3/3...)

I am also having this issue since the ixalan set was released. removing command tower did not fix it for me.

I am seeing this across most of my Historic decks, and I don't use Command Tower.

I have also experienced this issue, and as soon as I remove "Command Tower" from my deck, my deck no longer shows the status of non-format.

I have the same problem since the release of LCI. The card that seems to be causing this problem is 'Command Tower', because the error disappeared when I removed that card from one of the decks that showed a non-format error. However, only 6 of my HB decks show this non-format card error, but all my HB decks use 'Command Tower', which is kinda weird.