It looks like that could be it.
Here’s my Xcode Header Search Paths from Projucer built using commit c3e7c4725277b95363d68c3275d3bf2df78e2f0a from Oct 19:
You can see the AAX headers and my custom VST3 SDK.
But here’s my Header Search Paths from Projucer built using 2593d5e264d7a41dd98c40991d4694444f49adad from Nov 2:
Notice, no AAX headers and no custom VST3 SDK.
@ed95 ?