tl;dr – There’s a duplicate file somewhere in the project! Go hunt it down and destroy it mercilessly!
Ok, for all those in the future with this issue; this is what the problem was.
I had made BlahDataController months ago. About a week ago, I restructured the folders of the project and moved BlahDataController from a folder called “Blah” to another folder called “Data”.
When I changed the code for BlahDataController within the “Data” folder, one of my classes could see the changed code, however, another class couldn’t.
What ended up being the issue was that when I moved BlahDataController, it actually created a copy of it. So I had a BlahDataController in the “Data” folder, and an older BlahDataController in the “Blah” folder. Even though the older BlahDataController was no longer attached to the project in the project manager (left side of xcode), the fact that the physical file still existed in the folder caused this issue.
After deleting the duplicate older copy of BlahDataController, the issue was resolved.