I’ll start by saying this exact thing happened to someone else, I’ve liked a description of what happened to them

https://www.reddit.com/r/MagicArena/comments/1l8qqyy/bug_in_arena_cost_me_7_mythic_wildcards_has_this/

I redeemed some wildcards for a brawl deck. For some reason in took the amount of cards the deck would have originally took, rather than the few I still wanted. If you read the Reddit post you’ll see what happened. The screen looked funny before I crafted, so I took a screenshot. I only care about the rares and mythics. I have a before picture showing how many wildcards it took, and an after, showing the edits I made.

This cost me 80 rares and 13 mythics. If it’s a problem to import wildcards, feel free to incraft anything I’ve done in the past, I move on from decks pretty quickly.