Started manually vacuuming after removing pool cover and opening pool for season. I noticed that vacuum head was not picking up much dirt/leaf debris from bottom as usual. I started investigating why. I discovered when I connect the vacuum hose to the port in skimmer, a fist sized air bubble/pocket forms in pump strainer lid. (Maybe this is normal, as I’ve never looked in the past) The pump maintains prime, and there is a fair amount of suction created at the vacuum head. I have replaced my vacuum line and checked for air leak at strainer lid (Used shaving cream around the perimeter of lid) No improvement nor air leak found. When I disconnect the vacuum hose, the air pocket/bubble goes away.