I had the constant air bubbles thing happen to me about 13 years ago on a Cadillac STS...

Only went thru half a bottle until I stopped to think about WTF was going on...

Fluid moving thru an impingement will create low pressure due to Bernoulli principle, the opening of the threads of the bleed nipple internal to the caliper are at 90 degrees to the flow direction, thus will create a slight Venturi & suck in air thru the threads, especially when you're banging on the caliper with a rubber mallet