Anti Ice
Just to highlight the information that is crucial to answer the original question:
The Airbus descent profile is calculated for the situation "Engine Anti Ice ON during the whole descent."
If actually, you have Engine Anti Ice OFF during a (large) portion of your descent, you will always fall short on energy. Cause - with EAI ON, your idle N1 is slightly increased, giving you slightly more thrust.
Reason for calculating with EAI ON: Airbus wants to protect you from arriving at the bottom of your descent with too much energy, which could happen if calculation was made with EAI OFF while actually during descent EAI was used (ON).