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the failure is only seen sometimes. Repeatable failures are likely to be DUT-related and should be investigated and resolved as such.
the failure is because a transient is seen with the wrong timing i.e. the fail could be resolved by moving the mask in the x-axis (elapsed time) by no more than two seconds. Any failure because the time error amplitude is greater than allowed by the mask when they are aligned in the x-axis is a true fail and should be resolved in the DUT.
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