There should be more information on what went wrong in the logs of CouchbaseLite1. I can’t tell what is happening at first glance, and the description mixed with those log entries is very strange.
The only reason for a 404 on the changes feed is that the database does not exist on the other side, but it obviously does if you are replicating creations to and from it. My sneaking suspicion says that you are deleting the database on CouchbaseLite1 accidentally somehow. That would cause this behavior, but I don’t see any of that in the code you provided so I’m left scratching my head.