Submitted by elprofesor, also found by WatchPug, Koustre, cmichel, JMukesh, and pauliax
The use of transfer()  in Swap.sol   may have unintended outcomes on the eth being sent to the receiver. Eth may be irretrievable or undelivered if the msg.sender   or feeRecipient   is a smart contract. Funds can potentially be lost if;
The latter situation may occur in the instance of gas cost changes. The impact would mean that any contracts receiving funds would potentially be unable to retrieve funds from the swap.
This issue directly impacts the following lines of code:
Examples of similar issues ranked as medium can be found here and here, just search for M04. A detailed explanation of why relying on payable().transfer() may result in unexpected loss of eth can be found here
Manual review
Re-entrancy has been accounted for in all functions that reference Solidity's  transfer() . This has been done by using a re-entrancy guard, therefore, we can rely on  msg.sender.call.value(amount)`  or using the OpenZeppelin Address.sendValue library
Shadowfiend (Tally) acknowledged
