Is this skimmer setting in a sump? Then feeding to the return pump, and that locline is attached to the return pump? I suppose it is, if so when the skimmer is on, then the flow is increased in that compartment. So anything in that compartment can be lifted back into the column. And through the baffles and into the DT. Likewise if the return pump has a slow flow through it, then bubbles can collect in the line. Well, debritous can too, as well as critters. If somehow the skimmer is creating more pressure through the line, ie increasing the flow through it somehow, increasing the water level in the return compartment, then these things can be dislodged from there hold.