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
I managed to solve such a problem.
Identical or very similar.
Being at a advanced stage of creating the composition,
midi tracks started playing on their own.
All I had to do was select one and after turning on play, it would start playing certain repetitive patterns on its own
which clashed with what was actually written on the trace.
After about an hour, I discovered that the problem started when I started Chord Truck.
After deleting Chord Truck, the problem disappeared.
I hope this tip is useful to someone.