We have seen the same issue for multiple users using the same feature on Android devices. We get the internal sync replica error, however newly created data is PUSHed back to the service. DELETE's are not.
Aaron Dick
Switching to upload only no longer throws the error and data is Pushed up. Switch back to bidirectional and Sync, no error, and data created as well as DELETED are pushed.
This doesn't explain what the root cause of the issue is.