Just a heads up so you don't have to spend as much time as i did trying to figure out why collision rules seemed suddenly broken!
On my project I eventually figured out that if "movable" was turned on for both actors, collisions work. Most of my collisions involve only one "movable" actor, and the rules weren't being triggered.
I've got too many actors and I don't want to have them all movable (when I know it worked with only one movable actor), so personally I am going to try to roll back GS.
But might be a solution for others.