Conflicts not sending to Server until re-run the app

I am using Couchbase mobile lite 2.1.2 in iOs Swift, sometimes I am getting conflicts and showing error like below


CouchbaseLite Sync ERROR: {Push#1} Proposed rev ‘-J9xRmnIlvM1_r7izDM0fMJ’ #15-c3d0b50c6d9d8bdd11026b39cd0b85a441b4a34e (ancestor 14-8117ea690ba689491aa5d523fa8fc5fd) rejected with status 409

CBLReplicator[<*> URL[ws://ipaddress/default/]]: error pushing ‘624fe135-726b-4d39-8353-c51080bae2c0’: Error Domain=CouchbaseLite Code=10409 “rejected by server” UserInfo={NSLocalizedDescription=rejected by server}


But most of the errors are auto fixed and send to the server through sync gateway, but sometimes one or two conflicts are fixed and not sending to the server, when I re-run the app, those are sending to store.
Because of this application working very weird behavior.

Please assist me.