Replication doesn't sync doc for upgrade from 1.4 to 2.1.0

[hrajput89]

I installed the app for 1.4 CBL (iOS) and created few docs. Docs are getting synced to both SG(1.5) and CBS(5.0). Then I upgrade the cluster to 2.1 (SG 2.1 and CBS 5.5) and also update CouchbaseLite Framework to 2.1 using the feature/2.0 branch. App gets deployed but the changes or new docs are not getting synced from CBL app (iOS) to SG and CBS.

Scenario Workflow -

1. Install 1.4 todo app with 1.5 cluster.
2. Create few docs and check if they are syncing to CBS and SG
3. Update CBS and SG to 5.5 cluster
4. Checkout feature/2.0 branch and deploy the todo app with 2.1.0-233 build.
5. Check that if any new docs created are syncing to CBS and SG. Also check the any mutation to old docs are also getting reflected to CBS and SG

CBL Logs are available here -
https://gist.github.com/hrajput89/d4d07e130ea4c5e25293f56fef3f6749