I added some more assertions in sample and fixed tests which should show where your solution fails.

The problem is that since all the version methods operate on the same instance, rollback() also should alter the VersionManager instance. Your solution returns another instance on rollback() which works with chaining but not with separate method call like the random tests are performing.

It's difficult to tell what is wrong with your solution without seeing your solution.

But how do you know that your local test is correct?

It's difficult to tell what is wrong with your solution without seeing your solution.