...
... see if anything has been reported to Yamaha, ...
-my prediction: "really?.. that's the first time we hear about this happening... did you maybe spill water over keyboard?..."
@
AkkiMy advice would be (because keyboard is
new), that you return it to seller. That is, I wouldn't sent it to service, because it could take a while while before you get it back.
As for what could be the reason, it can be anything... defect Live Control potentiometer (happens),.. these potentiometers are soldered directly on board, so there could be (so called)
cold contact (you'd need soldering iron and experience to repair)... could be some loose contact on some connector (quite hard to locate)...
PS. Just saw you saying you turned off the message popping. Keep in mind that this only solves visual part of the problem. The thing is, this message only comes up if Live Control setting changed (that is, keyboard act as you actually did turned the knob).
Bogdan