If a statement has an external id / core prop with the value twice (as in here, the same value with different qualifiers), you get something like this:
wikidataintegrator.wdi_core.ManualInterventionReqException: "More than one WD item has the same property value Property: P486, items affected: ['Q18556300', 'Q18556300']"
If a statement has an external id / core prop with the value twice (as in here, the same value with different qualifiers), you get something like this: