Couchbase index gone/disapperar

We have 3 couchbase server with one replica on bucket.
We have created one index. So in indexes section, it show 2 index with different ip as we have one replica.

But many times happens, that after one node goes down. and after doing rebalance, only 1 index shows.

@ketan, which couchbase server version are you using?

Also how many index nodes do you have? And how do you create this index?