Answer: The only possibility that comes to mind is leaf miners. They small insects tunnel into the leaves of the peppers and create dead areas that might appear like blisters. The best defense is to grow the peppers under a floating row cover such as Reemay, at least until the summer when the heat gets high, then you'll have to remove it. This may help with your problem. I assume you know what leaf miner damage looks like, so if it doesn't fit the bill, the only other idea would be environmental stresssuch as lack of water. I guess you'll have to experiment with different solutions for find the best one.
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