In 3.4, there is a keystring version change. This will cause the following possible scenario:
1. User upgrade to 3.4
2. User create a collection in 3.4
3. User downgrade to 3.2 and attempt to start the server.
4. Server crash due to incompatible keystring version on the index.
We need to update dochub link (name: "3.4-index-downgrade") when downgrade grade with appropriate section exists that will give them user-friendly instruction on how to remedy this issue.