If I make changes to a header file in XCode 10.1, XCode doesn’t seem to be detecting it properly. I need to do a clean and then build to get the project to run without crashing. Anyone else having this issue?
yes I’ve seen and it has driven me crazy 
I mention it here:
also a weird thing about the new build system is that changes to the ofApp.h file don’t seem to be recognized. for example, I can type this into the the h file and it still compiles.
I recommend switching to the legacy compiler as discussed here:
this fixes a ton of issues and gets Xcode acting like normal. I think we should figure out what the issue is with the new build system but in the meantime this helps a lot.
Specially on iOS, some changes in code (without even changing headers) sometimes causing problems unless a clean is done first. 
OK, glad I’m not going crazy. Thanks for the workaround @zach! Another related annoying new “feature” , is that if you click on a compile error in a header file in the Issue navigator tab, you don’t get taken to the place in the file where the error is.