P3, P5, P7 are all on one side of the CPU, so it's likely the cooler pressure on the CPU IHS isn't even for some reason.
Some ideas:
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Use more paste and make sure the paste imprint is even.
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Double check to make sure you didn't mix the LGA1200/1700 standoffs which are different lengths.
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Make sure the excessively large universal Arctic mounting frame isn't catching on a VRM component.
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Make sure the contact frame tension is even across all four screws