Surround Mixing--VST Multipanner not working

When routing a quadro to a quadro track Cubase used to use the VST Multipanner, but now it’s randomly using MixConvert v6.

Why is this happening? How do I force Cubase to use the VST Multipanner?
Cubase Not using VST Multipanner.png


Reported to Steinberg CAN-32766. Thank you.