I've only just noticed this, but claiming the Arena Vouchers from my messages after earning them from the Intensive Shopping level 2 achievement didn't actually give me any. I had 57 both before and after claiming from the message.
While I can't 100% confirm, I don't think I've gotten any of them. Looking back, I should have earned 25 vouchers total from achievements so far (+Benchwarmers lvl 2 & Did You Use Bone Paste? lvl 1). I think I started with something in the high 20s, which would mean if I got those additional 25 from achievements then I would have had to place very low during all the arena battles to end up with 57 total. But I was getting first place most of the time. Also my We're Rich! achievement counter says I've collected 30 vouchers total. So I'm pretty sure the vouchers I have are only from the arena, and none of the achievement ones were rewarded.
Maybe because the Arena Vouchers don't actually seem to go in your inventory like the other weekly tickets do? Might be causing an issue with the claiming method?