Hello,
1. Please contact Player Support and have them delete your 4+ faction decks. This will resolve the issue for you.
https://support-legendsofruneterra.riotgames.com/hc/en-us
2. To all readers, please do not use external sites to create decks over the region limits to produce codes and then import these 4+ faction decks that you can't play in any modes. You will save yourself from encountering this bug. Very few players have ever done this, so this issue is currently limited to a handful of players. All of you may have upvoted this post :)
We will be fixing this bug in an upcoming release to prevent others from accidentally entering this state.
Thanks for the share, as always.