Main.storyboard forces Xcode to re-index and re-build the project non-stop

I inherited an Xcode project that targets iOS 12+, with source code written in Swift 4.2, and UI created using storyboard. The project compiles without errors, bur whenever I access Main.storyboard, Xcode would start re-indexing and re-building the entire project, repeatedly.

What might be causing this problem?
First thing, always, when opening a legacy project with a new version Xcode is to use the Product menu to clean the build folder.

Otherwise be sure that locations/paths involved aren't permission locked, and that you have several tens free space on your drive so that Xcode can do it's work without having to start over.
Main.storyboard forces Xcode to re-index and re-build the project non-stop
 
 
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