Scope cannot be properly estimated
Scope cannot be properly estimated due too many unknowns, complexity or missing details or issues with estimation accuracy
Discovered by combination of metrics:
Velocity: Committed vs. Completed, when team constantly overcommits and undercommits
Average Velocity, when average velocity is not stable / fluctuating without any changes in team's setup
Backlog Health, when low indicating that there is no enough "ready for development" scope to fill out several future iterations due to the fact that team cannot estimate work
Sprint Plan Change, high percentage of items being added or removed due to overload or under-load of the team during active iteration
Delivery Forecast via Burn-up, when "Scope" line is unstable, especially when Scope creep is high, also when "Completed" line is often very different from its overall trend