When "Disable Squiggles" is true, Visual Assist underlines mistyped symbols when you enable "Underline mistyped symbols". So you can disable the VA setting as a workaround.
However, when "Disable Squiggles" is false, Visual Studio underlines the mistyped symbols so Visual Assist don't need to. It will also solve the problem you had presented. Note that "Disable Intellisense" should also be false if you want Visual Studio to underline errors.