Could be a number of reasons that the state elements are not initialized. To figure out which elements are uninitialized you can do "init -show". If you want to debug why they are not being initialized you can do "debug -init". This will bring up an empty waveform window that you can add whatever signals you like.
As for the impact of these uninitialized elements, formal will perform an exploration with these elements being 0 or 1. In the case where a state element is supposed to be initialized and is not, you could potentially end up with false failures with the cause being an unexpected initial state.