Submitted by zzzitron, also found by GalloDaSballo
https://github.com/Tapioca-DAO/tapioca-bar-audit/blob/2286f80f928f41c8bc189d0657d74ba83286c668/contracts/markets/bigBang/BigBang.sol#L315-L316 
https://github.com/Tapioca-DAO/tapioca-bar-audit/blob/2286f80f928f41c8bc189d0657d74ba83286c668/contracts/markets/Market.sol#L340-L344
As an example, when calling BigBang.liquidate() the tx potentially fails, because the subsequent call to Market.updateExchangeRate (BigBang.sol line 316) can face a revert condition on line 344 in Market.sol.
In Market.updateExchangeRate() a revert is triggered if rate is not bigger than 0 - see line 344 in Market.sol.
Liquidations should never fail and instead use the old exchange rate - see BigBang.sol line 315 comment:
But the liquidation transaction can potentially fail when trying to fetch the new exchange rate via Market.updateExchangeRate() as shown above.
This issue applies for all markets (Singularity, BigBang) since the revert during the liquidation happens in the Market.sol contract from which all markets inherit.
Because of this issue users collateral values may fall below their debt values, without being able to liquidate them, pushing the protocol into insolvency.
This is classified as high risk because liquidation is an essential functionality of the protocol.
Here is a POC that shows that a liquidation tx reverts according to the issue described above:
https://gist.github.com/zzzitron/90206267434a90990ff2ee12e7deebb0
Instead of reverting on line 344 in Market.sol when fetching the exchange rate, consider to return the old rate instead, so that the liquidation can be executed successfully.
0xRektora (Tapioca) confirmed
