Regarding any unplanned work (defects, bugs, etc) do we really need to estimate?
This may make sense if we are adding work to the backlog for future consideration, but mid-Sprint, if this is one of those burning issues, then does it make sense to estimate, or does it makes sense to forecast the ability to complete it within the Sprint, assess its impact on the Sprint Goal and the PBI's that are associated to it, and self-organize as a team to complete it?