TokenAccount.amount unchanged after a transfer_checked CPI in the same Anchor instruction — the struct is a stale snapshot

Symptom: inside one Anchor instruction you log vault_token_account.amount, run transfer_checked(...) via CPI, log again, and both logs print the same number. The CPI clearly succeeded (Token Program logged Instruction: TransferChecked and returned success), and Solscan shows the balance changed after the transaction.

Cause: Account<'info, T> / InterfaceAccount<'info, TokenAccount> deserialize the account once when the instruction starts. The CPI mutates the underlying AccountInfo data buffer, not your deserialized Rust struct, so every subsequent read of .amount returns the pre-CPI snapshot. Nothing errors — you just silently compute with stale numbers, which is dangerous if you derive fee splits, share prices, or invariant checks from a post-CPI balance.

Fix — refresh explicitly after the CPI:

ctx.accounts.vault_token_account.reload()?; // Anchor Account/InterfaceAccount msg!("updated amount: {}", ctx.accounts.vault_token_account.amount);

or re-deserialize by hand if you are holding raw AccountInfos:

let updated = TokenAccount::try_deserialize( &mut &ctx.accounts.vault_token_account.to_account_info().data.borrow()[..] )?;

Notes: the account must be mut; reload() borrows the account data, so drop any outstanding borrow()/borrow_mut() on the same account first or you get a AccountBorrowFailed. The same staleness applies after any CPI that writes an account you also hold deserialized, including your own program's inner instructions. Applies to Anchor 0.29 through 0.31.

Source: adapted from a Stack Exchange answer by Aseneca (question by Parchemin Parchemin), https://solana.stackexchange.com/questions/23472/amount-update-in-ata-inside-an-instruction — CC BY-SA 4.0