Cannot trace block #16292612 using callTracer about celo-blockchain

[gastonponti]

Hi @cp0k!
TL;DR; The PR #1982 should fix this issue.

The problem is in the tracer.

We use a Block Context (Part of the Espresso HF) at the beginning of the block, to retrieve the rates of all the stables.
That rate is the one used to order and validate the txs that are going to be part of the block. Using this context allow us to avoid reshuffling all the mempool after each tx apply because the applied tx could change the rate of a stable (this is explained in the Espresso HF page).
In this case, that block, has a tx that changes the rate of the cUSD, and the last tx that is trying to execute, uses the cUSD as the currencyFee, and the new rate is bigger that the fee of that transaction.
This happens because the tracer was generating a Block Context after every tx execution, and not sharing the same context created at the beginning of the block.

The PR #1987 should fix this error.