Any time I open skillet with the new 2.4 (live) patch, the game locks up. I think it's trying to scan for recipes, but is getting stuck somehow. I let it sit for several minutes a few times, same thing every time.
If I recall, on every patch, Blizzard clears the local cache directory for Wow on your PC. All of the cached information for receipes will need to be downloaded from the server again. If the server is laggy, this can take quite a while especially if your have two professions with lots of items. I think engineering and alchemy have close to 300 combined items. I crashed out of the PTR a couple of times with ATSW which does the same thing.