Of the various MS-PDFT methods, compressed multi-state PDFT (CMS-PDFT) has been shown to have the best balance of computational efficiency and accuracy for the widest variety of systems, and it computes PESs similar to the more expensive extended multistate complete-active-space 2nd-order perturbation theory (XMS-CASPT2) for a variety of test cases. However, during the development of CMS-PDFT analytical gradients, it was discovered that CMS-PDFT struggles with linear molecules with degenerate 1 ∆ u states.