My biggest issues have been 1) Lack of a development community and 2) Both too much documentation and not enough.
1) The Mac dev forums from Apple are almost dead. Asking a question on StackOverflow is a literal crapshoot as to whether you'll get an answer or not. I don't know where to begin looking for an active, vibrant Mac developer community.
2) Apple's documentation is simultaneously rich and deep while being incredibly sparse, inconsistent, and maze-like. Very frequently you can find a description on SO or a blog post referencing something you need, yet the link is broken because Apple is very bad about maintaining and forwarding links when they change their URL structure.
There are entire classes of questions that I don't even know how to research or ask about yet I know should have answers when I encounter them.
Not too long ago I was doing something with AVFoundation. There was a particular setting that I needed to change, and by looking at the signature of a similar feature that plugged in the same way I knew it should be there. But I couldn't find it. The docs in this feature said nothing about it. I searched high and low for 2 days for sample code or anything that implemented this thing. I was getting nowhere.
I finally went back and watched the original 2 WWDC videos where AVFoundation was being introduced in 2011. After 2 hours and literally in the last 2-3 minutes of the 2nd video, the speaker casually mentioned the feature I was working with. I about flipped my lid at that point.
The property was exactly where I expected it. Xcode wasn't autocompleting it for some reason and I think there was a camel-case issue that was making it fail. All in all it was extremely frustrating.
I'm being vague about the details because this all happened about a year ago and I haven't thought much about it.
If anyone knows if/how you can display a window in the app while recording the screen with AVFoundation and not record that window, you'd save me a ton of time and frustration. Otherwise I fear I have to stop using AVFoundation and do my own implementation which I think is a very bad idea.