I've recently built a new machine and am using windows 10 so I'm not sure if that has anything to do with it but on this machine I have the latest AE2015 installed and noticed my timeline wont let me scrub and see my files moving in the windows. On my other machine on 2014 and before it would always live update but for some reason now I have to ram preview in order to scrub which if I have a project with a lot of layers in annoying to do everytime I make a change. I checked my settings live update is checked is there something else I need to click?
Do you have maybe layer with Trapcode Particular? I had the same issue, I updated Particular now it's fine!