I'm getting this problem in 11.2.1 under Yosemite - haven't updated yet, but 11.2.1 was fine under Mavericks and Mountain Lion.
However, I find that it does become responsive again... albeit after about 5 minutes have passed.
On this machine (i7 Macbook Pro 2.2ghz 17") I often get the problem where I get a playback error, and afterwards playback is garbled. The usual fix is to change the buffer size. Obviously that's not an option any more
