When you place the same weapons in different slots, there is a weight difference

[DixaxY]

As seen in the picture, I placed the same weapons in different slots. The weight changes. (I marked it with marks for better understanding).

When the same weapons in the 1st and 2nd slots are swapped, the weight does not change, this is normal. However, when they are swapped with the 3rd slot, it calculates the weight of the item placed in the 3rd slot.

While the total weight in the first picture is 159, when the same weapons are swapped in the second picture, the weight became 144.

[DakotaDust]

The weapon your character is holding changed. So yes, the weight changed.

[DixaxY]

but when the item in the 3rd slot changes, the weight changes.

[DakotaDust]

If that’s happening, your pictures don’t show it. You show your character hold a weapon, then swap weapons, and a highlighted version of pic 2.