UPDATE: OS X El Capitan 10.11.1 resolves an issue that prevents certain Audio Unit plug-ins from functioning properly.
I have a good reason why I usually upgrade to the latest Mac OS on the day of releases...
...because people want to know if Logic Pro works or not!
(It's usually best to refrain from updating your OS until the dust settles.)
You might want to bookmark this thread:
Mac Rumors: OS X El Capitan: Working & Not Working Apps