Gaps in Xcode build timeline

Reposting (after a while) from the Swift forums - the build timeline for our project has a lot of weird gaps in the beginning - almost 15 seconds in total, which is quite a big chunk of the total build time. Is there any way to determine why they exist or how I could fix them? I hope it's just something hidden and not the build system literally doing nothing...

This is on Xcode 15.4.

Gaps in Xcode build timeline
 
 
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