I guess this was one of those weird bugs with Xcode that you can’t trace or reproduce every time. I narrowed the issue down to one specific UILabel in the IB. As soon as I connect it to an IBOutlet UILabel *, I get this error.
On further investigation, it turns out that name title was causing the issue. I had the label declared as
IBOutlet UILabel *title;
As soon as I changed the name to gtitle, everything worked as expected. Who knows?..