Since this started (if so?) when you replaced the pads I wonder if you somehow got an air bubble in a bad place, ie. behind a piston.

The key to bleeding is to use gravity to work air bubbles up to the bleed port, or at least close enough to get pushed out early in the process.

If you've ever watched a nurse work a bubble out of an IV, you'll have seen how they tap the line to walk the bubble upward.

Also be sure to do the entire process methodically lest you somehow reintroduce air when finishing.