Storyboard doesn't display assets after migrating to Asset Catalog

After migrating image resources to an Asset Catalog the app builds and runs correctly but the assets don't show up in Xcode's storyboard.

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Solution

In my case this occurred because I used the full asset name including file extension (i.e. '.png') in Storyboard.

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However, the name for the asset needs to match the name of the Image Set in the Asset Catalog:

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So by removing '.png' from the image name in Storyboard it solved the problem.