What assumptions are made for the built-in Phase Shifter measurements?
The phase shifter measurements (PhsShift, PhaseErr, etc.) assume that phase only increases or only decreases as you progress through the states in order. If this is not the case in your design, the results of these measurements will not make sense. The reason for this is that phase reversal is currently not performed automatically. The way to tell if your phase is non-monotonic is to use the Phase measurement Linear > Port Parameters > S with AngU checked. This will show you where phase suddenly goes from increasing to decreasing or from decreasing to increasing unexpectedly.