Couchbase 5.1 Enterprise Edition - Rebalance stuck

I’ve a 5 nodes Couchbase standard cluster running on CentOS 7.0. After restarting a node, cluster was auto failed over and had to rebalance. The rebalance stuck always at around 20% progress. Stop and started few times but no luck. It always stuck on one Bucket. When I check that Bucket I could notice there are some vBuckets pending.

Any idea on what is happening here?