I just created a few new CPP & header files in the Projucer, clicked save project, then loaded one of these up in XCode. I was surprised to find that XCode was throwing up errors. All my includes in these header files were creating “file not found” errors. And the reverse was also true: my older header files were unable to reference these new header files.
My first instinct was to remove the references from the project, and then click “add existing files”. But the new CPPs and headers were not there! Weird. So, I did a bit of searching and found that the Projucer had saved them in a totally different folder, from which I had recently imported some binary files.