Discount with two roles in same user are being cumulative

I have 2 problems with the calculation of discounts.

I have 2 roles, one with different discounts in all categories and another role with special discount in category Filters. The first one 50% and the second one 55%.

The problem is that the user with both discounts have a price with the 50%, and then applies a 55% discount to the sale price. So a product price 100€ shows 22.5€. when should be 45€. I have changed the radio options in setting when user with multiple users roles assigned but nothing changes.

The other error comes with the same situation of discounts. If I add a discount by user (not role) for this user all discounts assigned to his role disappears, for other categories different to user discount.

I hope you can help me with this. Thank you.