Why is my hand pump pulling air?
The ale could still be highly conditioned some cask conditioned beers take a lot longer to clear down than others, it usually takes about,24, 48 hrs or even longer, but at the end of the day, it all depends on the brew.
Also change the hop strainer or washer that connects to the tap, sometimes this lets air through, make sure both the Jubilee clips are tight (the one that connects to the gas pump as well as the one connecting the pipe to the nut by the cask tap.
If you are not using a gas pump and it is a high lift maybe the weight of the ale in the line could be pulling air in somewhere from either the joints or the Beer engine cylinder itself. ..