In the RToken::burn function, the amount variable represents the amount of crvUSD that the user wants to withdraw, while userBalance refers to the balance of RToken that the user possesses. These two values are not comparable because the RToken amount and the crvUSD amount do not have a 1:1 ratio.
This leads to incorrect calculations.
Manual review.
Convert userBalance to a non-scaled amount by multiplying it by the index before making the comparison.
It's underlying vs underlying
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