Submitted by DadeKuma, also found by joestakey, Kumpa, CRYP70, and 0xTraub
https://github.com/code-423n4/2023-01-popcorn/blob/main/src/vault/adapter/abstracts/AdapterBase.sol#L529-L542 
https://github.com/code-423n4/2023-01-popcorn/blob/main/src/vault/Vault.sol#L447-L460
This issue applies to both AdapterBase.sol and Vault.sol. For the sake of simplicity and brevity, this POC will describe just the former.
Fee calculation is wrong and it either takes too few or too many shares than what is supposed to be when calculating the accruedPerformanceFee and the shares decimals are not 18.
The former causes a loss of shares that the FEE_RECIPIENT should earn, but the latter causes hyperinflation, which makes users shares worthless.
accruedPerformanceFee doesnt take into consideration the shares decimals, and it supposes that its always 1e18.
This is supposed to be a percentage and its calculated as the following, rounding down.
This calculation is wrong because the assumption is:
which is not always true because the totalSupply decimals can be greater or lesser than that.
Lets see what would happen in this case.
Best case scenario: supply decimals < 1e18
In this case, the fee calculation will always round to zero, thus the FEE_RECIPIENT will never get the deserved accrued fees.
Worst case scenario: supply decimals > 1e18
The FEE_RECIPIENT will get a highly disproportionate number of shares.
This will lead to share hyperinflation, which will also impact the users, making their shares worthless.
Modify the fee calculation so its divided with the correct denominator, that takes into account the share decimals:
RedVeil (Popcorn) confirmed, but disagreed with severity 
LSDan (judge) decreased severity to Medium 
