Load errors in merge preview of non-conflicting changes

Project ID: `3ML4PSdYv7vS467ZQ29bqs5pjkKw`

@jgbourque and I both branched from main. On "Justin's remix", Justin added some coins and some platforms, then merged back to "main" (commit 78313f0). On "More Platforms", I also added some new platforms, but I took care to renumber the nodes so that the names would not confict with Justin's changes.

When I preview the merge from "More Platforms" to "main", I see the following load errors:

Duplicates shouldn't have happened because the names I chose were distinct from all those on main.

If I close `main.tscn` in the editor before clicking "merge" to get the merge preview, this error is not displayed until I open `main.tscn`.

@jgbourque sees the same so I don't think it's bad state in my working copy, but just in case it is: [moddable-platformer_bad_merge.zip](https://github.com/user-attachments/files/25797695/moddable-platformer_bad_merge.zip)