When you feed the tank, you are changing the water tension so the skimmer will drop. When you change the water flow in the tank, the water tension will also change so the skimmer will drop. It usually is a temporary issue and the skimmer will return to normal in a few hours BUT if you adjust the skimmer after it has dropped, then what will happen is that when the water tension goes back to normal and the skimmer normalizes, since you have raised it, then it will overflow.
What you need to do is to make sure that the skimmer is working correctly before you feed the tank. After that, if the skimmer drops, just let it be and it will be back to normal in a few hours.
Also, make sure that you do not turn on the skimmer until the water level in the sump is back to normal. If the water level is higher than normal, the skimmer will overflow regardless.