So I think there is definitely a bug with the phase shift display in ReaEQ.
Take this example with a notch filter at 1khz. A notch filter should present a 90° phase shift at 1khz since the correlation being measured is no signal to full amplitude signal, which is 90° rotation.
Taking a measurement confirms this
This is taken with REW and shows the expected 90° shift at 1khz.
Testing against
DMG Equilibrium, which has a free phase design mode, confirms the REW measurements are correct.