Hi.
I'm having the same error in Magento 2.3.
If bundle child have is in any Cart Rule discount logic, the discount goes to the bundle parent instead.
Example: Bundle item (simple product itself) when added to cart, it applies 10% discount, but when we add some Bundle Product that contains that simple product mentioned as his child in cart, the 10% discount is applied to entire Bundle Product, instead of only the bundle item price.
So, if anyone have any way to fix this, please share.