dyld error when using R.swift with SwiftPM in custom build configuration

[iHarnastaeu]

When building with a custom configuration (e.g. DebugStage), the R.swift plugin fails during the resource generation phase with the following error:

dyld[55220]: Library not loaded: @rpath/RswiftResources.framework/Versions/A/RswiftResources
  Referenced from: <...> /Build/Products/DebugStage/rswift
  Reason: tried:
    '/usr/lib/swift/RswiftResources.framework/Versions/A/RswiftResources' (no such file, not in dyld cache),
    '/System/Volumes/Preboot/Cryptexes/OS/usr/lib/swift/RswiftResources.framework/Versions/A/RswiftResources' (no such file),
    '/usr/lib/swift/RswiftResources.framework/Versions/A/RswiftResources' (no such file, not in dyld cache),
    '/System/Volumes/Preboot/Cryptexes/OS/usr/lib/swift/RswiftResources.framework/Versions/A/RswiftResources' (no such file)
Abort trap: 6
Command PhaseScriptExecution failed with a nonzero exit code

This only happens in the custom configuration. In the standard Debug configuration, everything works as expected.
Build settings between the configurations are nearly identical:

LD_RUNPATH_SEARCH_PATHS and FRAMEWORK_SEARCH_PATHS are the same.

The difference is limited to display names, bundle Ids and a few compilation conditions.

The plugin runs in both configurations, but only fails in the custom one.

Thanks in advance for looking into this!