I had almost the exact same symptoms this year when I started my pool
up, with the aquabug only cleaning part of the pool and the air in the
filter housing. In my case, it was indeed air leaking through the pipe
connections. I disassembled the connections between my skimmer and
pump, cleaned the gaskets, and reassembled everything tightly with
some teflon tape around the screw connections. Afterwards the flow with
aquabug attached, while still less than with the skimmer, is much
greater and doesn't have any air in it. My aquabug is moving noticably
faster and producing greater suction.