There was an adjustment made to how drop rates work a while ago where you get a reduced drop rate if you are a lot of levels above the thing you are killing, it was intended for the purpose of stopping high level players camping mid level bosses, so they were available for newer players to enjoy. But I'm wondering if maybe the same effect is causing you to have an extremely low drop rate if you're a lot higher level than the bandits. If that's the case, then I think it's not intentional and should be considered a bug, GM should make some adjustments to the drop logic so it doesn't affect things like this. Back in the day these would usually drop after 2 or 3 kills