Apple Time Capsule/Time Machine - Where did my 136GB go?

On an Apple Time Capsule, I changed the file sharing settings from “With device password” (where everybody uses the same password) to “With accounts”. Before the change, 136GB was in use.

I created two accounts.

The Time Capsule created two shared folder. User1 can only see the new empty folder “User1”. And User2 can only see the new empty folder “User2”.

There is still 136GB unavailable. It’s useless, nobody can see it, it’s just hogging a huge chunk of the drive.

Any ideas for recovering that space?