Celestian; I was helping Giuly on Discord with this and there does seem to be an issue with such an effect. I wasn't sure if it was intended or a bug.
As Giuly says adding the effect to a weapon seems to be missing out the ATK: 2 bit. The effect appears correctly on the CT and shows that it is being applied correctly to the CT from the weapon in question. However the +2 isn't added to the attack roll if the PC targets an appropriate type of creature and then double clicks the attack roll. Interestingly if I drag and drop the attack the EFFECTS +2 appears in chat but still doesn't get added to the attack roll.