Immobilize buff
It was probably buffed to make it consistent with other conditions, there was no way to intuitively know that immob behaved differently than all other conditions, which was bad design (especially with skills like Devourer Venom where one strike canceled out the other).
Immob is in a weird state now IMO since while it is op in some situations, in other situations classes can get 100% reduction on it, rendering it (and other CC conditions) useless to any class that doesn’t pump +100% duration.