Your “real code” and the examples are using different packages. The “real code” encounters a twisty gap in the method tree of my GenericSchur package, which I will address in the next release. (Thanks for your accidental contribution, and sorry for the inconvenience.)
A possible workaround for now is
import LinearAlgebra.eigvals
eigvals(A::Symmetric{BigFloat}) = eigen(Hermitian(A)).values