Early on, it seems like Heisenberg's uncertainty principle was regarded as a principle of ignorance. That is, it says what's possible to measure or to know, rather than what actually is.
However, since its discovery, the uncertainty principle has predominately been interpreted as a principle of indeterminacy. That is, it's not just that we can't perfectly measure an electron's position, rather it's that the electron doesn't have an exact position.
Is the original epistemological interpretation still valid, or are there other reasons to believe that quantum properties are really indeterminate, i.t. not just unknowable?