There’s a glitch with the vault cards. If you get a crate that has more cards than your vault can hold you lose all of them above your 300 max. I’ve lost almost 150 cards due to crossing the threshold of increasing tier when my vault was almost full.
Additionally it’s too expensive for common cards.
Hey @kavaea thanks for reaching out! This is intended, your vault can only hold a certain amount of bonus cards, once that 300 mark is reached, the bonus cards from crates are lost. You'll need to open your vault and start filling it up again if you want to collect all bonus cards possible.