Air getting into pump

I have a recent development where air is getting into the pump housing somehow and pushing out to the spa. I can't tell if it's coming in through the pump or elsewhere. So far I have tried different pump lids (with different o-rings), and still the problem persists. I know the most obvious answer is that the lid seal isn't solid, but I'm not sure what else I can try to get a more "tight" seal. I'm worried about overtightening and causing something to crack. I took a video showing that the water is not fully filling the housing and also the bubbles entering the spa.