AppCode has also become increasingly buggy over the last year or so, and is now almost as unusable as Xcode (albeit in different ways).
On my computer, recent versions of AppCode constantly use at least 100% CPU, even when it's in the background doing nothing. I got this a few times in earlier versions as well, but an "Invalidate caches and restart" usually fixed the problem. No such luck with recent versions. It will always use at least 100% when it's running.
I often get 30 seconds of beachball when I switch back to AppCode from some other app, despite having 16GB of RAM and not running any other remotely heavy app. This will happen even if I just leave AppCode for half a minute in order to check something on a web page. It's gotten so bad that I've developed the habit of checking web pages on my iPad instead of on my Mac, in order to avoid temporarily leaving AppCode.
There is a particularly infuriating bug that will sometimes cause AppCode to freeze when I type the opening parenthesis of a function invocation. When this happens, killing, restarting and typing again won't work, AppCode will freeze at the same spot. The only workaround I have found when this happens is to type my function invocation in some other editor and copy and paste to AppCode (often after waiting the usual 30 seconds for AppCode to stop beachballing).
It is not just me – all my coworkers suffer from the same problems. AppCode is by far the most annoying app I use on a daily basis. I hate it nearly – but not quite – as much as Xcode.