CouchDB 2 DBs (bidirectional replication) missing seq in _Changes

I have 2 DBs in 2 CouchDB Servers.

Server A (Couch 1.3), mydb (original)

Server B (Couch 1.6), mydb (newly created)

those 2 dbs are bidirectional continous replication using _replicator docs

I wanted to see certain seq from _Changes but Server A has seq but it doesn't exist in Server B.

Here's the result. serverA/mydb/_changes?since=234904&limit=1

{"results":[
{"seq":234905,"id":"e8b98f98d17ba4a4188c4ef49d4cc3cf","changes":[{"rev":"2-6769c1f434e0aafeeb5f37bc62cbd6a1"}]}
],
"last_seq":234904}

serverB/mydb/_changes?since=234904&limit=1

{"results":[
{"seq":234907,"id":"e8bdasfdff44335g5esg46uk7o86edg4","changes":[{"rev":"2-67d3rfevre4566thfghfdye45223d6a1"}]}
],
"last_seq":234907}

As you see, Server A has seq 234905 but it doesn't exist in Server B.

I have a client(couch 1.2) that is replicating docs from Server_B/mydb which used to be Server_A/mydb and the client's replication status stuck at this sequence which i can not find. So I can't resolve this replication fail issue.

any idea?