When you attempt to import an FBX with the same name as another asset in the same folder, it asks to overwrite it. Many users and licensees use this method over our "Reimport" options because there are typically settings that they need to change that aren't available from the Skeletal Mesh details panel.
If they are attempting this overwrite reimport method and the reimport fails, there is a high likelihood that the existing skeletal mesh will be deleted.
1. Download the attached zip file and unzip it.
2. Import the fbx from the GoodFBX folder and save all the assets
3. Import the fbx from the BadFBX folder to the same Content Browser location
4. When it asks to overwrite, select Yes
5. After it fails, attempt to open the skeletal mesh
6. Go to another folder in the CB and back
Result: Skeletal Mesh has been deleted
Expected: Original Good Skeletal Mesh remains after a failed overwrite.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-24252 in the post.