When connecting to SQL Server, tables relationships are allowed on only one key. If the field is repeated, it will not consider it as unique though it is since there is more than one key in each tab...
there is already an idea for that - please vote for 10321815 composite-key-support-in-power-bi https://ideas.powerbi.com/forums/265200-power-bi-ideas/suggestions/10321815-composite-key-support-in-power-bi
