I play RS on Mac and I haven't had any freezing problems that weren't caused by bad customs. The game plays absolutely fine on Mac and there's nothing wrong with RS or Steam, or Yosemite. Sounds like you have some bad customs, and/or corrupted official DLC. Either that or something is wrong with your game installation. I would suggest clearing out all of the cDLC that you have and then check the integrity of the game cache to verify that RS is installed correctly. You can do this by opening Steam, right-clicking on Rocksmith 2014 and choosing "Properties". Then click on the "Local Files" tab and select "Verify Integrity of Game Cache". Most freezing problems are caused by cDLC that is improperly packed, uses the wrong AppID, or conflicts with other customs you have in your dlc folder. Official DLC that has been pirated can also cause problems. Thanks for your tip. "All files validated" was the answer. So everything should be ok? I use custom songs only, because they aren't offering that song in official store. I pay official songs, so I can sleep well and support developers. I think my next step is to remove songs, that I have put in DLC folder lately - so thank you again!