There’s always something new that Cubase does to stop me working on literally every project. Now, every empty sampler track and MIDI track are playing random notes on the 1st and 3rd beat. Is there a work around this? Apparently others are having the same issue 
Could it be something on the chord track? This always fools me.
Is it truly random or do the same unwanted Notes play?
I’d be suspicious that something is set to be included in All MIDI Inputs which should not be. @Kearley 's suggestion of the Chord Track is a good candidate too. Perhaps you could post some screenshots of a Track that is doing this and include its Inspector.
errrrrm !
silly question but …
do have a midi controler in your setup ??
if so is it set to All midi inputs ??
in fact check all your midi I/O for this ,
i had this once and it was my Qcon Daw controller it was set to transmit on "all midi " thus sounding sporadic notes , even if i did not touch the controller because the slightest vibration or a “dodgy” fader/knob/switch will be enough to send a midi mesage.
hope this works …good luck
Cheers
Tony