multiple track arming on Cubase SL & SX

I want to record more than 2 tracks of audio simultaneously on SL or SX. I used to be able to do this but now now I cannot arm more than 2 tracks at a time. I can arm tracks 1 & 3 but not 1 & 2 for instance. :neutral_face: I’ve checked everything I can think of. What can I have missed?

Correct # of input buses in VST Connections?