To be clear what I am referring to is the the stat drops from shadows and ghosts which, by your question, would fall under the +20 save vs negative effects. Either I really suck at saving throws or it isn't working as intended as I experienced stat drop after stat drop after stat drop. Consuming a lesser restoration removes the effect, but also gives an attack of opportunity to the attacker which dropped the stat again. My toon is a monk, with minimum stat scores of 12 so should have at least some saving throw bonuses overall.
I have also experienced 1 level drain while fighting ghosts in Gastria- with the negative energy protection potion being consumed just prior to the combat.
Mostly my concern is the stat drops. As Western Barovia has more of the stat drop attacks and not outright level drain attacks. ( I have only experienced level drain/s in Western Barovia from a vampire.) The stat after stat experience took place in the sullen woods were the shadows will drain strength. The herbalist next to the woods offers negative energy protection via spell to everyone who asks, yet if the spell has been changed she is effectively offering nothing based upon what I experienced.
In terms of mechanics game balance and making sure that negative energy protection can't for example deflect the spell Harm I can see the point of nerfing it. However Negative Energy Protection, a 3rd level spell, and by herbalism a lower level easy to make potion was the only protection from negative attack stat drops in the entire game minus of course, the much higher, only cast on self, arcane spell shadow shield.
If the change intended for a much reduced chance for a negative attack stat drop then I do not think it is working correctly from what I have experienced. I will also note that said experiences have caused my avoidance of the encounters since as the repeated unstoppable stat drops are not fun to try and escape from.
