How to reproduce:
1. Create a new project
2. Create 2 UI Document files (Create -> UI Toolkit -> UI Document)
3. Open one of the UI Documents and add 2 of the other UI Document in the Hierarchy (Library -> Project -> Assets -> Drag into Hierarchy)
4. Save the file
5. Delete one of the added UI Documents
6. Save the file
7. Observe the console

Expected result: No error is thrown
Actual result: Multiple errors are thrown for every instance still in the hierarchy and after closing and trying to reopen the file cannot be parsed

Reproducible with: 6000.0.61f1, 6000.2.0a7, 6000.2.10f1, 6000.4.0a1
Not reproducible with: 6000.2.0a6, 6000.3.0b8, 6000.4.0a3
Fixed in: 6000.4.0a2

Reproducible on: Windows 11 Pro (24H2)
Not reproducible on: No other environments tested

Notes:
- “Semantic - 'Template' declaration requires a 'path' or 'src' attribute referencing another UXML file” only gets thrown once
- “Semantic - Unknown template name “_____”” gets thrown for every instance of the duplicate UI Document instance