Artifact Traits are calculated and saved with the gearing strategies that you run.
Those two sets of gear are within 0.65% of each other. That is well within the target margin of error for Best in Bags, which is 1%.
Each individual simulation can give you an error in the 0.25% range, but the predictive model has to take into account stats, legendary items, set bonuses, trinkets, relics, etc. Getting within 1% is excellent and definitely working as intended.
You can certainly do your own spot-checks to squeeze out that last theoretical 0.5% or so DPS, but the instant BiB optimization can’t get that perfect.