Available now, this update fixes the long-standing sync bug on iOS 9. If you were bitten by this issue an update/reinstall should get things sorted out. Due to the nature of the bug we recommend starting with a fresh sync setup. Details on how to do that can be found in our Changing Sync Setup article.
This release also marks the transition to a new developer account. This is noteworthy because it means the new version will not have access to passwords stored in your keychain from the previous version. When re-establishing sync with Dropbox you may be asked to enter your sync password. If you don’t recall this password you will need to clear the sync setup and re-sync a fresh copy of your document. During this process you will have to the opportunity to provide a new sync password. For step-by-step instructions see Clearing Sync Setup in the Knowledge Base.
Additionally, this update contains lots of changes to lay the groundwork for future updates. You can check out the full release notes for more.