In the case of merge problems some portion of a YAML -format Unity file might be repeated more than once in an asset file.

If an object is repeated this will be reported with a message like:
Duplicate identifier 624274415. File: "Assets/DuplicateFileIDs.unity".

However when the file ID is greater than 2^31 (2,147,483,647) then the wrong value is printed, which can make it hard to pinpoint the problematic part of the file for manual repair.

Repro steps:

-Create a simple Prefab
-Open the prefab file in a text editor
-Find an object with an identifier that is more that 2147483647 (the id is randomly generated)
-Copy and past that object so it appears twice in the file
-Save the prefab file
-Refresh the asset database and click on the prefab

Expected Result: Several error messages will be logged, including one "Duplicate identifier " and quoting the correct id
Actual Result: the error message shows a seemingly random id, which might be negative

Context:

The identifier printed is the local file identifier, and corresponds to the first line of a serialized object within the scene, prefab or other asset file, for example:

"--- !u!1 &624274415"

By definition each object within a serialized file must have its own unique identifier. The most common cause of duplicate values is when a merge conflict or other operation on the text file has caused some portion of the contents to be duplicated within the file.