I've heard of people having all kinds of problems with Yosemite if they update from a previous version of OS X as opposed to doing a clean install and then re-installing your software. The update route can break all sorts of things. It might be necessary to do this (a clean install) to get things working properly again. Make sure to back up anything you don't want to lose first if you go this route. I did do a clean install of Yosemite and am experiencing no problems whatsoever. I have Logic Pro 9 and Logic Pro X running flawlessly on both a MacBook Pro with Retina display and a MacBook Air. Hopefully, you can find another fix to your problem but, if not, a clean install should get everything working again. There is all sorts of info on the web about how to do this...it's pretty painless. Good luck!!