PCA scores are uncorrelated because they come from the eigen-decomposition of the covariance matrix. When you rotate the loadings (e.g. varimax), the rotation matrix is orthogonal, so the axes remain orthogonal, but the scores no longer stay uncorrelated. This is expected as rotation trades uncorrelated scores for more interpretable loadings.
Hence, if you need uncorrelated variables, use the original PC scores, and if you need interpretability, use the rotated ones (and accept correlation).
