Thanks for the response. I understand the ambiguous data message means there are ambiguous names in the hierarchy. My dataset contains a single hierarchy of Country → State → City and I did verify the data a few times.
Some entries work correctly, but a few important ones like Sao Paulo, which the only city named Sao Paulo in the Sao Paulo state, doesn’t seem to go through Quicksight at all.
Here’s a screenshot of the map I can see in my analysis:

Here’s a small sample of cities that work and doesn’t (it returns 7 ambiguous values that honestly shouldn’t, given the names are accurate). I hope that trying it out with this sample and double checking with any map search will shed some light on the subject:
Country,State,City
Brazil,Sao Paulo,Sao Paulo
Brazil,Sao Paulo,Poa
Brazil,Sao Paulo,Cotia
Brazil,Sao Paulo,Guarulhos
Brazil,Sao Paulo,Pompeia
Brazil,Sao Paulo,Sao Carlos
Brazil,Minas Gerais,Belo Horizonte
Brazil,Minas Gerais,Sabara
Brazil,Minas Gerais,Araxa
Brazil,Minas Gerais,Uberaba
Brazil,Minas Gerais,Juiz de Fora
Brazil,Maranhao,Sao Luis
Brazil,Goias,Anicuns
Brazil,Goias,Goiania
Brazil,Goias,Planaltina
Brazil,Goias,Trindade
Brazil,Goias,Morrinhos
Brazil,Goias,Rio Verde
Brazil,Rio Grande do Sul,Porto Alegre
Brazil,Rio Grande do Sul,Sao Leopoldo
Brazil,Rio Grande do Sul,Santo Angelo
Brazil,Rio Grande do Sul,Santa Maria