See the discussion in the Scala flowdock, but the tl;dr is there's an overloading ambiguity:

    ambiguous reference to overloaded definition, both method getter in class Symbol of type 
    (base: ScalaPresentationCompiler.this.Symbol)ScalaPresentationCompiler.this.Symbol 
    and  method getter in class SymbolContextApiImpl of type => ScalaPresentationCompiler.this.Symbol 
    match expected type ?