try_inverse_mut documents:

Attempts to invert this square matrix in-place. Returns false and leaves self untouched if inversion fails.

For matrix sizes 5 and above, the implementation is:

                    let oself = self.clone_owned();
                    lu::try_invert_to(oself, self)

In turn, lu::try_invert_to(matrix, out) documents:

If matrix is not invertible, false is returned and out may contain invalid data.

So it looks like Matrix::try_inverse_mut may fail to keep its documented promise to leave self untouched