Submitted by csanuragjain, also found by rbserver, 0xSmartContract, btk, joestakey, Josiah, Viktor_Cortess, rvi0x, RaymondFam, Deivitto, KIntern_NA, 0xNazgul, 0xdeadbeef0x, koxuan, 0xNineDec, pavankv, Rolezn, Bauer, and UdarTeam
If you are making a Lock fund for escrow using a fee on transfer token then contract will receive less amount (X-fees) but will record full amount (X). This becomes a problem as when claim is made then call will fail due to lack of funds. Worse, one user will unknowingly take the missing fees part from another user deposited escrow fund.
Compute the balance before and after transfer and subtract them to get the real amount. Also use nonReentrant while using this to prevent from reentrancy in ERC777 tokens.
RedVeil (Popcorn) confirmed 
