GoToDefinition is not working for some identifiers in VisualFSharp.sln

[dsyme]

Open VisualFSharp.sln, then open PatternMatchCompilation.fs, go to computeWhatSuccessfulTypeTestImpliesAboutNullTest and select go-to-definition on TypeNullIsTrueValue

let computeWhatSuccessfulTypeTestImpliesAboutNullTest g tgtTy1 =
    if TypeNullIsTrueValue g tgtTy1 then
        Implication.Nothing
    else
        Implication.Fails

Expected: navigation

Actual: "Can't navigate to symbol"

Other symbols seem available, so it's unclear to me what the problem is

[dsyme]

The symbol is resolved, but this call is failing to find the target symbol in the document:

                let symbolUses = checkFileResults.GetUsesOfSymbolInFile targetSymbolUse.Symbol