That's a lot of food to give a BP back to back. My guy is on a 5 day schedule, and I don't handle him or touch him at all for 2 days after feeding. It lets them get settled in after a meal. If you think that his current meal isn't enough, just try giving him a larger meal the next time.

If the problem persists, then you'll be able to find several threads on tricks on problem feeders. As for now, you should stop giving him food every 3 days. I understand you want him to take one of those times, but he has no urgency to eat when he knows there will be food shortly. When they don't eat, just remove the mouse/rat and wait til his next appointed feeding time. You could even wait a couple days longer just for the hunger to set in. Good luck though.