The object used for performing yielding captures the point for the clock from the original OperationContext, so it cannot be used for the clones of the stages meant to run in a separate thread unless we double check that the clock is thread safe (the main OperationContext should already survive until all the threads have been stopped). Alternatively, change PlanYieldPolicySBE so that it uses the clock from the OperationContext that is provided at runtime and avoid providing one in the constructor