Answer: There is no reasonable explanation for one plant to not set fruit when an adjacent plant is setting fruit as it should. For some reason the non bearing plant is not being pollinated. You can try spraying the open blooms with Blossom Set (available in garden centers). Some tomato varieties do well in the heat and humidity and others don't so make note of the variety that is producing well and plant that same variety next year - but don't bother with the other. Hope you have a great harvest!
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