Theft of high-value items and in-game currency from characters

I haven’t logged into the game for 2 days, but when I entered the game, I didn’t find any expensive items on my main league character, and all the currency and cards were missing from the chest. Also, all the expensive items disappeared from the character and the chest, as well as all the currency in the standard league. There were no unauthorized entries under my Steam account. How could this have happened???