Sometimes, users incorrectly deposit cryptocurrency - by either using the wrong deposit address or missing certain information (i.e. memo field in currencies like XRP). This causes those deposits to become "lost in transit", and thus will not reflect on your Liquid account.
Liquid can attempt to retrieve these tokens, but delivery cannot be guaranteed, and a significant administrative fee can be charged
Fees Incurred by Retrieval Service
Type of Missed Deposit
Deposits of tokens into correct address, but missing Destination Tag
Deposits of tokens into incorrect addresses
Currently, Liquid’s ERC20 unified MPC-based deposit wallets makes it so that today, all ERC20’s and ETH deposits share the same deposit address, thus eliminating any ERC20-based deposit problems. You can read more about this technology here.