Hi,
No, it’s not necessary to deactivate these 2 Max virtual MIDI Ports. If you are not using them as an remote device in Cubase, it’s OK.
I see, if you are not using Max virtual ports as a substitution of the CMC-FD MIDI In/Out, then it’s not related to my post. But to be honest, I don’t know, if the IAC driver is not affected by the same issue too.
And I would guess, Cubase really tries to connect to the CMC In/Out automatically when starts. :-/