Sacred 2:Faster Increase of Survival Bonus
This modifier has gone through a journey of a lot of myths for what it does:
Contrary to the name of this modifier, it does not increase the rate the player gains their Survival Bonus. In the days of CM-Patch, it was believed that this modifier directly increases your survival bonus, so in the Community Patch, the name of this modifier is changed to "Survival Bonus" +X% to more accurately describe what it does, but the numbers don't fit with the numbers you're seeing ingame when equipping an item with this modifier.
It has been suspected that this Bonus might instead directly multiply your ingame combat time. Since the formula for your Survival Bonus is S=T/(T+6), where T is your ingame combat time measured in hours, from there we could calculate that the formula for what this modifier actually does would be:
S_2=(BS+S)/(BS+1) where S is your Survival Bonus without the modifier, S_2 is your Survival Bonus with the modifier and B is the modifier bonus.
So e.g. a Survival Bonus of 50% and a "Survival Bonus" +X% of 30% would result in a new Survival Bonus of (0.5*0.3+0.5)/(0.5*0.3+1)=(0.65)/(1.15)~56.52%
And indeed that would fit the numbers we're seeing ingame.