Hello Miguel,
I cannot know your pricing condition and procedure configuration specifics, so I will try to give you some example from IDES, which might help you find out what is the case in your system.
Here is a screenshot of the initial situation in my sales order - PR00 (price), RB00 - discount as supplement for PR00.
I will first add PN00 (price at item level) as 300 EUR/1 PC. It will deactivate PR00 and RB00, which will show as inactive with Y, because you cannot have more than one active price condition.
I will add PMIN (condition class A) as 25 000/PC. I will not deactivate PN00, because this is not configured as price (B), but it will change the net value with the formula assigned in the pricing procedure (it is also possible to set inactive status for conditions with VOFM routines, but here I am using only the standard setup).
Now if I maintain HM00 (header price) as 400 EUR, PR00 and RB00 will be still inactive with Y, but because we have to set 400 as price, PN00 will be deactivated with Y, but the same will happen with PMIN, because it was used to set netwr, which we now change.
Exclusion groups are just one of the ways to deactivate conditions - similar effects can be achieved with VOFM routines, I have seen people add the logic in user exits, last active price needs no specific configuration to use it.