Thank you for reporting a bug to Unity.
After reviewing the behavior, we've confirmed it aligns with the current design and intended use of the feature. We understand this may differ from your expectations or workflow.
Animation clips are path-based. Since there is no way to differentiate between two siblings with the same name, the Animation System will animate the first one it finds. This is by design, and aligned with FBX behaviour. If you wish to avoid this, rename your object.
We will close this case as 'As Designed.' If you have feedback on how the feature could better meet your needs, please let us know - we value your input and consider it in future improvements.