How do I debug Xcode's incremental build issue?

Hi, I have a project where I notice that without any changes, when I do a do a second build, there are certain files keep being rebuilt. Only when I do a third build (again without any changes) does Xcode finally recognize nothing needs to rebuild.

Are there any debug flags I can turn on to get Xcode tell me what makes it decides to rebuild a file?

How do I debug Xcode's incremental build issue?
 
 
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