Survivorship Rules and OV Calculator

Why am I getting two different values - one OV value for the MDM and one OV value in GBQ or Qubole?
Why is the nested attribute value using singleValueByCrosswalkSources being overridden when the aggregation has been applied?
Why do I see two different values for an attribute for the same source on a crosswalk when I am using LUD survivorship?
How does order of data load affect the OV?