Xcode storyboard: Internal error. Please file a bug

I had the same issue. Got it fixed using below steps :

1. Delete the derived data of your project

2. Clean your project (Shortcut : cmd + shift + k)

3. Now, run your app.

Clearing out the DerivedData folder (in ~/Library/Developer/Xcode/DerivedData) is what fixed the issue for me.

The following steps will stop your problem.

1. cmd + shift + k
2. cmd + option + shift + k
3. Restart Xcode
4. Restart Mac.

I faced the same issue. And it was solved by cleaning up the build files.

cmd + shift + k

AND

cmd + option + shift + k

Hope this helps Thanks.