Wrong free product

I have a 4+1 free discount rule. When buying any 5 products in our store, they get the cheapest for free. I have set it up with Buy X Get Y, and it works. The cheapest product is free.

But there is a problem. I also use Sales Booster Order Bumps, that gives a big discount of product P on the checkout page. When adding product P on the checkout page, product P is changed to the free product, because that is now the cheapest product in the basket. That’s not what I want of course.

I have tried to use the following filter in the Buy X/ Get Y rule: Filter product NOT in list Product P. But this doesn’t work. These filters ony works in a way that this product doesn’t count for the X quantity, but what I need is to exclude product P as the free gift given within this Buy X/Get Y rule.

How do I exclude a product (or several products) for Y (instead of X)?