[CBM] 'connection refused' when backing up during a rebalance

What's the issue?
I was running continuous backups during rebalances and hit a connection refused error when bootstrapping (via gocbcore). The logs for the failed run, and scripts used during testing can be found attached to this issue. This issue appears to be somewhat reproducible.

Setup
4 nodes, 3 with KV
3 buckets each with 64 vBuckets and 500,000 items