It looks like you're losing connective tissue between the polyps. This is commonly referred to as XXXX Tissue Necrosis. You'll hear a lot of Rapid or Slow tissue necrosis being said. With that being said, it isn't "polyp bailout". This is where the polyp completely lets go of the skeleton to float away. They can later reattach to the substrate and grow a new skeleton. You might want to read around the SPS Forum here on Reef Central. Acropora, like you have, will go through this on their way to the big beyond.