Myserm's last successful login was almost 3 years ago and there were certainly no login attempts for it yesterday (or this year in general).
Can you please tell us when you attempted to buy the pack and what the account was? None of the accounts you've named so far ever had 20 ST to begin with.
While there might be a chance that you stumbled on some weird shop bug that took away your ST but never added the item nor created a transaction for the log, there's no way that every time you received Shiai Tokens the shop was broken - and only for you alone.