An action item can be invisible due to a missing check in regard of Future/Mod aspect

function Inventory:EquipActionItem(item)
    if item == nil then
        item = self:GetActiveItem()
    elseif item ~= nil
        and (item.components.inventoryitem == nil or
            item.components.inventoryitem:GetGrandOwner() ~= self.inst) then
        return
    end
    if item ~= nil and
        item.components.equippable ~= nil and
        item.components.equippable.equipslot == EQUIPSLOTS.HANDS then
        if not item.components.equippable:IsEquipped() then
            if item.components.stackable ~= nil and item.components.stackable.stacksize > 1 and not item.components.equippable.equipstack then
                local stack = item.components.stackable:Get(item.components.stackable.stacksize - 1)
                self:GiveItem(stack)
            end
            self:Equip(item)
        end
        if self:GetActiveItem() == item then
            self:SetActiveItem()
        end
    end
end

For example, this function does not check the result of Equip, thus the active item may not be equipped correctly, making it lost forever in limbo state.