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I don’t know that. Maybe its a bug of the HD Tune Pro tool v5.50.
Did you get similar problems with other benchmark tools like ASSSD or Anvil’s Storage Utility?
Addtionally I would like to know the chipset of your mainboard and the OS you are running. Please put such infos into your signature.
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It will never do that. A secure erase of the SSDs and a fresh OS installation will - if doing anything - enhance the performance.
As I already have wriiten, I suspect a bug of the HD Tune version you have used or an incompatibilty with your special system.