Troubleshooting & messages · Free space and clean-up messages
Why does it say my Mac wasn't ready to let go of space held in automatic backups?
Short answer: Storage Studio asked, but macOS decides what to release and wasn't ready (often because a backup hasn't reached Time Machine). The space usually returns on its own within a day.
Storage Studio can ask macOS to release space held in its automatic backups, but macOS makes the final decision. Sometimes it keeps them — for example, if a backup hasn't been copied to Time Machine yet.
Nothing is wrong. The space comes back on its own, usually within a day. If it's urgent, you can delete individual local snapshots in the Local Snapshots section after reading its warnings.