Hello,
I am not sure but based on our discussion in the comments, and the version you are using 2.0.1, I guess that the index is not up to date when it is called by your application (during/just after rebalance)
I will invite you to move to 2.1 or 2.2 to be able to use the new “consistency” feature we have added in it:
http://docs.couchbase.com/couchbase-manual-2.2/#disabling-consistent-query-results-on-rebalance
Regards
Tug
@tgrall