CouchbaseLite/REPLICATOR: process rev has invalid ancestor

We ran into issue where documents were not. sycning to the tablet, We got the logcat and show it was logging below error:-

CouchbaseLite/REPLICATOR: {N8litecore4repl6PusherE#770} Proposed rev 'TestDoc::b920b374-925f-4915-8bc5-a223aceae2c8' #1-c798c5d430359f2a24ca9d23777e17c2 has invalid ancestor 1-c798c5d430359f2a24ca9d23777e17c2

I am completely new to couchbase, i need to undertstand what will cause this issue and how can i prevent this from happening?

The above is just a warning at the level of CouchbaseLite and it should be coming from Sync Gateway. Could you please provide the Sync Gateway logs associated with the above?