I just had the same issue. After a few hours scratching my head and trying all kind of things, I finally found a fix: remove the whole package 'project.xcworkspace' inside the XXXXX.xcodeproj package.
More specifically, when you find the 'XXXXX.xcodeproj' file, right-click it, and select 'Show Package Contents'. This will get you inside the package where you will find the 'package.xcworkspace' file. It is best to do this while the Xcode project is closed.
Maybe that will work for you or for others with the same issue in the future...
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