I'm almost 11 weeks out and I still get water blisters and sores pretty often on the hard and soft palate. I also can feel when this happens the hard palate gets a bit inflamed and puffy. It seems to be either:

1. food that is acidic (not necessarily acidic food you would expect). Juices burn sometimes, tomato sauce has to be chased with milk, ginger, too much pepper, etc

2. food that is hard, crunchy or sharp. It seems to irritate or cut the inside of the mouth.

I usually just deal with the pain when it comes up, but it is pretty annoying. Hopefully it will continue to improve.

Interestingly, the blisters and sores only appear on the side of my mouth that received the greater amount of radiation (my left side). The hard palate feels completely different across the midline when it is inflamed and blistered.