Hello there,
I have a somewhat similar problem with using the APC mini. With the sliders I got other additional midi messages (B0 ...) appearing in the preview window. Sometimes QS acts like it is receiving slider control change messages and shifts random sliders by one or two percents on own initiative. It's tricky with the rotation knobs on live events. The shift is invisible on the virtual knob but the laser cues start appearing flatter or distorted.
Happened four times on live events when I've gone to take pee (lol) setting the software to automatic mode (VirtualLJ) and by getting back the controller was freezed out completely and was not reacting to anything. Had to restart the QS.
After a twenty minute of use it begins being late with the feedback lights. Late enough to show the FX pad for seconds after release. Sometimes the Shift On/Shit Off is being reverted.
It was reproduced on four different computers, on Win7 and Win10 either, with and without external powered usb hub. It seems that the controller lights are unstable and blinking unnatural. The phenomenon is not so severe with other softwares but I can get random blinks on the pad.
I called the service this week, they told it unseen that the controller is fine, the software must have the problem. However, I suspect something with the controller, too.
While composing this post, I accidentally reproduced the issue posted above by mortenx.
After a short time, everything is back to normal, without closing the QS.