The XRP protocol is the set of rules governing XRP ledger transactions. in general all software using the ledger (e.g. wallets, validators (transaction servers)) must follow the rules or risk having their transactions rejected.
In May of 2020 the XRP Protocol was amended to allow for deleting accounts.
The more frequent use of the AccountDelete transaction generates regular support requests as the balance of the deleted goes 'missing'.
Despite strong, clear warnings on utilities like XRP ToolKit users assign exchange XRP accounts as the balance destination sometimes even diligently including the correct destination tag for their exchange account.
Warning from XRP ToolKit Account Delete Screen
While exchanges are commonly set up to properly credit their customer's exchange account for XRP received in a Payment transaction type (if the correct destination tag is in the correct field), they seem less prepared to handle the AccountDelete transaction type sending customers scrambling for support.
Often, customers report the exchanges telling them the XRP are 'lost'.
Of course, the funds are never 'lost'. They are on the ledger. They never have been/will be anywhere else.
Access to the funds may be compromised if the account holder mismanages the account credentials or if a transaction gets mis-routed.
The second case is commonly what happens when the balance from an AccountDelete transaction gets sent to an exchange.
Exchanges that aren't set up to route an AccountDelete transaction type receive the balance in their exchange XRP account but don't credit the customer account.
The situation can be compounded by lack of knowledge on the part of the exchange's support resources who don't consider the AccountDelete transaction type when trying to resolve the situation.
Exchange support resources also may not have the tools to search their XRP accounts by transaction type.
XRPL Labs can't help directly with this situation.
Remediation can be achieved by providing the exchange support with the Transaction ID from the AccountDelete transaction.
Some XRP ledger explorer sites also don't seem prepared to parse and display AccountDelete transactions erroneously showing them as 'inactive' (i.e. having no reserve which is accurate but incomplete) or even saying they don't exist.
Bithomp is one that does correctly display (on desktop) the account information and the AccountDelete transaction itself. Entering the account address of the deleted account should bring up the history showing the AccountDelete transaction ID necessary for the exchange to track the transaction.