any specific function ?

here i can see .sub operations in this code block.

add a check for :

require(afterDeposit >= beforeDeposit, "");

before doing:

_amount = afterDeposit.sub(beforeDeposit);

add similar checks here :

`totalZaifInPools = totalZaifInPools.add(_amount).sub(depositFee);
user.amount = user.amount.add(_amount).sub(depositFee);
pool.totalLp = pool.totalLp.add(_amount).sub(depositFee);`

** If Possible use hardhat console logging, so that you can debug easily
then it will be easy to debug