Alchemix Transmuter

Summary
In StrategyMainnet.sol checking the balanceOf the asset in the contract after transmuter.claim is inccorect and causes the function to always revert

Vulnerability Details

balBefore is set after claim which is incorrect since it cant keep a track of the tokens in address(this)
Since trasmuter.claim transfers tokens to address(this) the amount is updated, the exchange doesnt do anything that will cause a change of this count since it exchanges 1:1 from the underylying to synthetic token. This improper place for getting balanceOf the contract then results in faul in

https://github.com/alchemix-finance/v2-foundry/blob/master/src/TransmuterV2.sol#L238-L250
https://github.com/alchemix-finance/v2-foundry/blob/master/src/TransmuterBuffer.sol#L345-L363

Proof that claim actually transfers tokens (WETH) to address(this). and thats why the balanceOf should be updated before calling claim

require((balAfter - balBefore) >= _minOut, "Slippage too high");

Impact

Not being able to Claim underlying token like WETH and swap it back to Alchemix token.

Tools Used

Recommendations
Update the balanceOf before calling transmuter.claim