Based on the recommendation from the Consultancy plan 

Since the Install team frequently encounters unplanned work that needs to be added into the sprint, a suggestion for the team is to track that unplanned work over a period of time to get an average amount of unplanned work. Use that average when sprint planning to determine how much capacity the team should set aside for unplanned tasks, and how much to commit to. If fewer unplanned tasks come in than expected, work can be pulled in from the backlog.  

Suggested steps:

• Track number of unplanned customer issues/bugs over the next 3 sprints.
• Use that to determine an average estimate of unplanned bugs / work that come in each sprint.
• Based on that, set aside some capacity during sprint planning to account for the unplanned work.