I ran into this problem and after a couple of days of looking for solutions I found the cause. The Preview Assets.xcassets file was in the custom Resources folder, the path to which I specified in BuildSettings - Deployment - Development Assets "myApp/Resources". I created a "Preview Content" folder and moved the Preview Assets.xcassets file into it, also replaced the Development Assets config with "myApp/Resources/Preview Content" and the problem went away. Apple magic.
alekseyho
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