Help

OK need a little help I've done a quick video as well to show what im on about

I've vaccum bagged my lay up and got absolute vaccum, but when I do a drop test leaving it 15min when I come back to it turn the pump on and release the clamp it starts pulling vaccum again then after a few minutes it pulls absolute vaccum again without touching anything,

Is this normal or is something causing it to do this? I don't want to infuse it if airs getting into the bag

Thanks Paul