Hey sigoru!
There are generally two reasons content is removed from your account -
If a player participates in Refer-A-Friend fraud to acquire IP or RP, then any champions/skins gifted with this IP or RP are removed.
If a player purchases RP and gifts content with it, and subsequently issues a chargeback for the money spent on that RP, we will remove that content.
If you believe that content you have purchased/received on your account has gone missing and is not due to either of these two scenarios, make sure to submit a ticket! We can look into your account and investigate further!